Method of producing a silicon compound material and apparatus for producing a silicon compound material

ABSTRACT

Provided is a method of producing a silicon compound material, including the steps of: storing a silicon carbide preform in a reaction furnace; supplying a raw material gas containing methyltrichlorosilane to the reaction furnace to infiltrate the preform with silicon carbide; and controlling and reducing a temperature of a gas discharged from the reaction furnace at a predetermined rate to subject the gas to continuous thermal history, to thereby decrease generation of a liquid or solid by-product derived from the gas.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of InternationalApplication No. PCT/JP2017/024511, filed on Jul. 4, 2017, which claimspriority to Japanese Patent Application No. 2016-134128, filed on Jul.6, 2016, the entire contents of which are incorporated by referenceherein.

BACKGROUND ART Technical Field

The present disclosure relates to a method of producing a siliconcompound material and an apparatus for producing a silicon compoundmaterial, and more specifically, to a method and apparatus for producinga silicon compound material, such as a silicon carbide-based ceramicmatrix composite.

Related Art

Silicon compound materials, particularly ceramic matrix composites (CMC)have attracted attention as materials which have light weight and areexcellent in mechanical strength even at high temperature, and theirmass production in the near future has been investigated. The ceramicmatrix composites are composites each obtained by infiltrating a preform(fabric) formed of ceramic fibers (reinforcing material) with ceramic asa matrix. Of those, a silicon carbide-based ceramic matrix composite(SiC-based CMC) using silicon carbide (SiC) for both the fabric and thematrix is excellent in light weight and high heat resistance, and isregarded as a leading next-generation material.

Hitherto, the production of the silicon carbide-based ceramic matrixcomposite has involved a chemical vapor infiltration (CVI) stepillustrated in FIG. 1. In the CVI step, methyltrichlorosilane (CH₃SiCl₃:MTS) and a hydrogen gas (H₂) serving as a raw material gas are supplied,and the raw material gas is infiltrated into a silicon carbide preformstored in a reaction furnace of a hot wall type in which an atmosphereis retained at a temperature of from about 800° C. to about 1,100° C.and a pressure of from about several Torr to about several tens of Torr.Thus, a silicon carbide matrix is deposited on the preform. In thereaction furnace, MTS forms the matrix by being precipitated in thepreform as silicon carbide through various intermediates (molecules).However, part of MTS forms the matrix, and a residual part thereof isdischarged from the reaction furnace. Some of the various molecules tobe discharged become polymers of higher-chlorosilanes when cooled toroom temperature, and are precipitated in an exhaust pipe or a pump.

Meanwhile, there is disclosed, in a method of producing trichlorosilanethrough conversion of tetrachlorosilane and hydrogen, a technology forsuppressing generation of polymers of higher-chlorosilanes by processinga reaction gas from a conversion furnace in a first cooling step, anintermediate reaction step, and a second cooling step (see PatentLiterature 1).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-Open No. JP2010-132536

Non Patent Literature

Non Patent Literature 1: D. Togel, A. Antony, j. Bill, Petra Scheer, A.Eichhofer, G. Fritz, Journal of Organometallic Chemistry 521 (1996) 125.

Non Patent Literature 2: Investigative Report of the Explosion & FireAccident occurred in the High-Purity Polycrystalline SiliconManufacturing Facility at Yokkaichi Plant of Mitsubishi MaterialsCorporationhttp://www.mmc.co.jp/corporate/ja/news/press/2014/14-0612.html

Non Patent Literature 3: Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.;Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone,V.; Mennucci, B.; Petersson, G. A. et al. Gaussian 09, revision D.01;Gaussian, Inc.: Wallingford, Conn., 2009.

Non Patent Literature 4: A. Miyoshi, GPOP software, rev. 2013.07.15m5,http://www.frad.t.u-tokyo.ac.jp/˜miyoshi/gpop/.

Non Patent Literature 5: A. Miyoshi, SSUMES software, rev. 2010.05.23m4,http://www.frad.t.u-tokyo.ac.jp/˜miyoshi/ssumes/.

Non Patent Literature 6: CHEMKIN-PRO 15131, Reaction Design: San Diego,2013.

Non Patent Literature 7: Yang-Soo Won, J. Ind. Eng. Chem., Vol. 13, No.3, (2007) 400-405

Non Patent Literature 8: E. A. CHERNYSHEV, et. al., Journal ofOrganometallic Chemistry 271 (1984) 129.

SUMMARY Technical Problem

In the CVI step in the production of the silicon carbide-based ceramicmatrix composite, a gas discharged from the reaction furnace containsvarious molecules derived from MTS, and some of the various moleculesare cooled to be deposited as a liquid by-product in the exhaust pipe.The by-product contains higher-chlorosilanes, and hence may combust whenignited or become an explosive substance in a solid form when oxidizedin contact with the atmosphere. In addition, the by-product alsogenerates gases, such as HCl and H₂, in contact with air.

Therefore, it is required to disassemble the pipe and immerse the pipein water to hydrolyze the by-product into silicon dioxide (silica),followed by washing. When the amount of the by-product deposited islarge and the by-product is not sufficiently oxidized inside thereof,the by-product has sometimes been ignited during the washing. Inaddition, the by-product having been collected is required to be put ina container and recovered by industrial waste disposal operators. Asdescribed above, the maintenance of an exhaust passage in the CVI stepentails a large burden and also requires cost.

Meanwhile, the technology disclosed in Patent Literature 1, which isintended to suppress the generation of the polymers of thehigher-chlorosilanes in the reaction gas from the conversion furnace, isbased on the conversion of tetrachlorosilane and hydrogen. Therefore,the technology is not applicable to the gas discharged from the reactionfurnace in the CVI step for the silicon carbide-based ceramic matrixcomposite.

The present disclosure is provided in view of the above-mentionedcurrent circumstances, and an object of the present disclosure is toprovide a method of producing a silicon compound material and anapparatus for producing a silicon compound material each capable ofdecreasing the generation of a liquid or solid by-product derived from agas discharged from a reaction furnace in which a silicon compoundmaterial, such as a silicon carbide-based ceramic matrix composite, isproduced by a CVI method.

Solution to Problem

In order to solve the above-mentioned problems, according to oneembodiment of the present disclosure, there is provided a method ofproducing a silicon compound material, including the steps of: storing asilicon carbide (SiC) preform in a reaction furnace; supplying a rawmaterial gas containing methyltrichlorosilane (MTS) to the reactionfurnace to infiltrate the preform with silicon carbide; and controllingand changing a temperature of a gas discharged from the reaction furnaceat a predetermined rate to subject the gas to continuous thermalhistory, to thereby decrease generation of a liquid or solid by-productderived from the gas.

The step of controlling and changing a temperature of a gas dischargedfrom the reaction furnace may include a step of retaining the gasdischarged from the reaction furnace at a predetermined temperature. Thepredetermined temperature may fall within a range of 500° C. or more andless than 950° C. or may be 1,500° C. or more. The predeterminedtemperature may fall within a range of 600° C. or more and less than800° C. The step of decreasing generation of a liquid or solidby-product may include retaining the gas discharged from the reactionfurnace at a predetermined temperature for a predetermined time periodfalling within a range of from 0 seconds to 8 seconds. The step ofdecreasing generation of a liquid or solid by-product may includechanging the temperature of the gas to a plurality of temperatures in astepwise manner.

The liquid or solid by-product may include a higher-chlorosilane. Thestep of decreasing generation of a liquid or solid by-product mayinclude converting SiCl₂ serving as a precursor of the liquid or solidby-product into a stable substance, to thereby decrease the generationof the liquid or solid by-product. The stable substance may include atleast one of methyltrichlorosilane, dimethyldichlorosilane((CH₃)₂SiCl₂), disilane (Si₂H₆), dichlorosilane (SiH₂Cl₂),trichlorosilane (SiHCl₃), or tetrachlorosilane (SiCl₄).

The step of decreasing generation of a liquid or solid by-product mayinclude adding a predetermined additive gas to the gas discharged fromthe reaction furnace. The step of decreasing generation of a liquid orsolid by-product may include adding the additive gas so that an amountof substance of the additive gas is larger than an amount of substanceof the liquid or solid by-product.

The step of decreasing generation of a liquid or solid by-product mayinclude adding chlorine so that an amount of substance of chlorine islarger than an amount of substance of silicon contained in the liquid orsolid by-product.

The step of decreasing generation of a liquid or solid by-product mayinclude a step of retaining the gas discharged from the reaction furnaceat a predetermined temperature, and the step of retaining the gasdischarged from the reaction furnace at a predetermined temperature mayinclude the adding a predetermined additive gas.

The step of retaining the gas discharged from the reaction furnace at apredetermined temperature may include using a reforming furnace, and atime period for which the gas discharged from the reaction furnace isretained at the predetermined temperature may be a residence time of thegas in the reforming furnace.

The predetermined temperature may fall within a range of 200° C. or moreand less than 1,100° C.

The predetermined temperature may fall within a range of 750° C. or moreand less than 850° C.

The additive gas may include a gas including a molecule containingchlorine. The additive gas may include at least one of a nitrogen gas(N₂), a hydrogen gas (H₂), hydrogen chloride (HCl), chloromethane(CH₃Cl), tetrachloromethane (CCl₄), trichloroethylene (C₂HCl₃),trichloroethane (C₂H₃Cl₃), ethylene (C₂H₄), ethanol (C₂H₆O), acetone(C₃H₆O), methanol (CH₄O), water vapor (H₂O), dichloromethane (CH₂Cl₂),or chloroform (CHCl₃).

In addition, the additive gas may include chloromethane ordichloromethane, and, in the step of retaining the gas discharged fromthe reaction furnace at a predetermined temperature, a time period forwhich the gas discharged from the reaction furnace, to which theadditive gas has been added, is retained at the predeterminedtemperature may be set to 0.08 second or more.

In addition, the additive gas may include chloromethane ordichloromethane, and, in the step of retaining the gas discharged fromthe reaction furnace at a predetermined temperature, a time period forwhich the gas discharged from the reaction furnace, to which theadditive gas has been added, is retained at the predeterminedtemperature may be set to 1 second or more.

In addition, the additive gas may include chloromethane, and, in thestep of retaining the gas discharged from the reaction furnace at apredetermined temperature, an amount of substance of chloromethane to beadded may be 1.0 time or more as large as an amount of substance ofmethyltrichlorosilane in the raw material gas to be loaded.

In addition, the additive gas may include chloromethane, and, in thestep of retaining the gas discharged from the reaction furnace at apredetermined temperature, the predetermined temperature may fall withina range of 750° C. or more and less than 850° C., an amount of substanceof chloromethane to be added may fall within a range of 1.0 time or moreand less than 1.5 times as large as a loading amount ofmethyltrichlorosilane in the raw material gas, and a time period forwhich the gas discharged from the reaction furnace, to which theadditive gas has been added, is retained at the predeterminedtemperature may be set within a range of 1 second or more and less than10 seconds.

In addition, the additive gas may include dichloromethane, and, in thestep of retaining the gas discharged from the reaction furnace at apredetermined temperature, an amount of substance of dichloromethane tobe added may be 0.25 time or more as large as a loading amount ofmethyltrichlorosilane in the raw material gas.

In addition, the additive gas may include dichloromethane, and, in thestep of retaining the gas discharged from the reaction furnace at apredetermined temperature, the predetermined temperature may fall withina range of 750° C. or more and less than 850° C., an amount of substanceof dichloromethane to be added may fall within a range of 0.25 time ormore and less than 1.5 times as large as an amount of substance ofmethyltrichlorosilane in the raw material gas to be loaded, and a timeperiod for which the gas discharged from the reaction furnace, to whichthe additive gas has been added, is retained at the predeterminedtemperature may be set within a range of 1 second or more and less than10 seconds.

In addition, the additive gas may include any one of hydrogen chloride,tetrachloromethane, trichloroethylene, trichloroethane, and ethylene,the predetermined temperature may be 975° C., an amount of substance ofthe gas to be added may be 1.0 time as large as an amount of substanceof methyltrichlorosilane in the raw material gas to be loaded, and atime period for which the gas discharged from the reaction furnace, towhich the additive gas has been added, is retained at the predeterminedtemperature may be set to 1 second.

In order to solve the above-mentioned problems, according to oneembodiment of the present disclosure, there is provided an apparatus forproducing a silicon compound material, including: a reaction furnaceconfigured to store a preform; a raw material gas supply portionconfigured to supply a raw material gas containing methyltrichlorosilaneto the reaction furnace; a reforming furnace configured to retain a gasdischarged from the reaction furnace at a predetermined temperature; andan additive gas supply portion configured to supply a predeterminedadditive gas to the reforming furnace.

In addition, the reforming furnace may be of a hot wall type.

In addition, the reforming furnace may have arranged therein a baffleplate.

In addition, the reforming furnace may be formed of a circular tube, andthe circular tube may have a specific surface area falling within arange of from 5 mm to 15 mm, which is determined by dividing a volume ofthe circular tube by a surface area of the circular tube.

Effects of Disclosure

According to the present disclosure, the generation of the liquid orsolid by-product which is derived from the gas discharged from thereaction furnace in which a silicon compound material, such as a siliconcarbide-based ceramic matrix composite, is produced by a CVI method, andmay become an explosive substance through a reaction with the atmospherecan be decreased.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual view of a CVI method.

FIG. 2 is a view for illustrating a construction guideline for aby-product generation reaction mechanism.

FIG. 3 is a view for illustrating a method of decreasing the generationof a by-product through use of a reforming furnace.

FIG. 4 is a view for illustrating a method of decreasing the generationof a by-product through introduction of an additive gas.

FIG. 5 is a view for illustrating a method of decreasing the generationof a by-product through use of a reforming furnace and an additive gas.

FIG. 6A is a first graph for showing a change in free energy ofhigher-chlorosilanes.

FIG. 6B is a second graph for showing a change in free energy of thehigher-chlorosilanes.

FIG. 7 is a view for illustrating a reaction path between SiCl₂ andanother gas species.

FIG. 8 is a view for illustrating a reaction path from 3SiCl₂ to(SiCl₂)₃.

FIG. 9 includes graphs for consideration of a polymerization temperatureof SiCl₂.

FIG. 10A is a first view for illustrating a main reaction of SiCl₂ atthe time of temperature reduction.

FIG. 10B is a second view for illustrating the main reaction of SiCl₂ atthe time of temperature reduction.

FIG. 10C is a third view for illustrating the main reaction of SiCl₂ atthe time of temperature reduction.

FIG. 11A is a first view for consideration of heat treatment conditionson an exhaust side.

FIG. 11B is a second view including graphs for consideration of the heattreatment conditions on the exhaust side.

FIG. 12A is a first graph for comparison of generation amounts ofhigher-chlorosilanes relative to a retention temperature.

FIG. 12B is a second graph for comparison of the generation amounts ofthe higher-chlorosilanes relative to the retention temperature.

FIG. 12C is a third graph for comparison of the generation amounts ofthe higher-chlorosilanes relative to the retention temperature.

FIG. 13 includes graphs for showing prediction of polymerization ofSiCl₂ in a MTS/H₂ system.

FIG. 14 is a graph for showing a diminution speed of SiCl₂ at the timeof retaining an exhaust gas at various temperatures.

FIG. 15 is a graph for showing a reaction rate constant k_(SiCl2) foroverall elimination at which a by-product can be eliminated fastest bycombining optimal conditions at each retention temperature.

FIG. 16 is a graph for showing temperature dependence of the maximumreaction rate constant k_(SiCl2) for overall elimination shown in FIG.15.

FIG. 17 is a view for illustrating a summary of conditions of reactioncalculation at the time of adding a gas.

FIG. 18 is a graph for showing a first gas addition effect at 600° C.

FIG. 19 is a graph for showing the second gas addition effect at 600° C.

FIG. 20 is a graph for showing a gas addition effect at 900° C.

FIG. 21 is a graph for showing a residual rate of CH_(4−n)Cl_(n) after aCH_(4−n)Cl_(n)/H₂ reaction for 1 second at various temperatures.

FIG. 22 is a graph for showing a change in partial pressure of gasspecies at the time of adding CH₂Cl₂ and retaining at 900° C.

FIG. 23 is a graph for consideration of an optimal addition amount ofCH₃Cl.

FIG. 24 is a graph for consideration of an optimal temperature at thetime of adding CH₃Cl.

FIG. 25A is a first view for illustrating a main reaction of a CH₃radical at various temperatures.

FIG. 25B is a second view for illustrating the main reaction of the CH₃radical at various temperatures.

FIG. 26 is a view for illustrating a reaction energy between SiCl₂ and aC-based molecule.

FIG. 27A is a first view for illustrating a reaction energy betweenSiCl₂ and a diene.

FIG. 27B is a second view for illustrating the reaction energy betweenSiCl₂ and the diene.

FIG. 28A is a first view for illustrating a cyclic (CH₂SiCl₂)_(n)structure.

FIG. 28B is a second view for illustrating the cyclic (CH₂SiCl₂)_(n)structure.

FIG. 28C is a third view for illustrating the cyclic (CH₂SiCl₂)_(n)structure.

FIG. 29A is a first graph for showing a change in free energy of cyclic(CH₂SiCl₂)_(n) at various temperatures (K).

FIG. 29B is a second graph for showing a change in free energy of cyclic(CH₂SiCl₂)_(n) at various temperatures (K).

FIG. 30 is a schematic view of an exhaust gas reforming experimentalapparatus.

FIG. 31 is a graph for showing a relationship between an amount of aby-product to be collected and a treatment temperature.

FIG. 32 is a graph for showing a relationship between the presence orabsence of a reforming furnace and a content of MTS.

FIG. 33 is a view for illustrating a configuration of an experiment fora by-product difference depending on a temperature of a reformingfurnace.

FIG. 34 includes appearance photographs of a liquid by-product andsilica.

FIG. 35 includes graphs for showing a by-product difference depending onthe temperature of the reforming furnace.

FIG. 36 is a conceptual view of exhaust gas treatment with an additivegas.

FIG. 37 is a view for illustrating a configuration of an experiment.

FIG. 38 is a graph for showing a mass balance.

FIG. 39A is a first graph for showing comparison of exhaust gascompositions at the time of decomposition at high temperature in thecases of using HCl, CH₂Cl₂, and N₂ as an additive gas.

FIG. 39B is a second graph for showing comparison of the exhaust gascompositions at the time of decomposition at high temperature in thecases of using HCl, CH₂Cl₂, and N₂ as an additive gas.

FIG. 40A is a table for showing examples of elementary reactions relatedto SiCl₂ and constants thereof.

FIG. 40B is a graph for comparison of the rate constants of elementaryreactions listed as candidates.

FIG. 41 is a view for illustrating simulation conditions.

FIG. 42A is a graph for showing the result of simulation in the case ofadding HCl as an additive gas.

FIG. 42B is a graph for showing the result of simulation in the case ofadding CH₂Cl₂ as an additive gas.

FIG. 42C is a graph for showing the result of simulation in the case ofadding CH₃Cl as an additive gas.

FIG. 42D is a graph for showing the result of simulation in the case ofadding C₂HCl₃ as an additive gas.

FIG. 42E is a graph for showing the result of simulation in the case ofadding C₂H₃Cl₃ as an additive gas.

FIG. 42F is a graph for showing the result of simulation in the case ofadding CCl₄ as an additive gas.

FIG. 43A is a graph for showing a change in partial pressure of SiCl₂depending on a residence time at various temperatures in the case ofusing CH₂Cl₂ as an additive gas.

FIG. 43B is a graph for showing the partial pressure of SiCl₂ at anoutlet of a reforming furnace.

FIG. 43C is a graph for showing a change in partial pressure of SiCl₂depending on a difference in flow rate ratio between the additive gasand MTS at various temperatures.

FIG. 44A is a graph for showing a change in partial pressure of SiCl₂depending on a residence time at various temperatures in the case ofusing CH₃Cl as an additive gas.

FIG. 44B is a graph for showing the partial pressure of SiCl₂ at anoutlet of a reforming furnace.

FIG. 45 is a graph for showing the partial pressure of SiCl₂ in the caseof changing the addition amount of CH₃Cl serving as an additive gas.

FIG. 46 is a graph for showing a mass balance calculated in Example 4.

FIG. 47A is a photograph in the case of not adding an additive gas.

FIG. 47B is a photograph in the case of adding HCl as an additive gas.

FIG. 47C is a photograph in the case of adding C₂HCl₃ as an additivegas.

FIG. 47D is a photograph in the case of adding CCl₄ as an additive gas.

FIG. 47E is a photograph in the case of adding CH₃Cl as an additive gas.

FIG. 47F is a photograph in the case of adding CH₂Cl₂ as an additivegas.

FIG. 48A is a graph for showing a relationship among the addition amountof CH₃Cl, the temperature of a reforming furnace, and the yield of aby-product.

FIG. 48B is a graph for showing a relationship among the residence timeof CH₃Cl, the temperature of the reforming furnace, and the yield of theby-product.

FIG. 48C is a graph for showing a relationship among the residence timeof CH₃Cl, the temperature of the reforming furnace, a flow rate ratio,and the yield of the by-product.

FIG. 49A is a graph for showing a relationship among the addition amountof CH₂Cl₂, the temperature of a reforming furnace, and the yield of aby-product.

FIG. 49B is a graph for showing a relationship among the residence timeof CH₂Cl₂, the temperature of the reforming furnace, and the yield ofthe by-product.

FIG. 49C is a graph for showing a relationship among the residence timeof CH₂Cl₂, the temperature of the reforming furnace, a flow rate ratio,and the yield of the by-product.

FIG. 50A is a photograph in the case of not adding an additive gas.

FIG. 50B is a photograph in the case of adding CH₃Cl as an additive gas.

FIG. 50C is a photograph in the case of adding CH₂Cl₂ as an additivegas.

FIG. 51 is a view for illustrating an apparatus for producing a siliconcompound material according to an embodiment of the present disclosure.

FIG. 52 is a view for illustrating a modified example of a reformingfurnace.

DESCRIPTION OF EMBODIMENTS

Now, with reference to the attached drawings, an embodiment of thepresent disclosure is described in detail. The dimensions, materials,and other specific numerical values in the embodiment are merelyexamples used for facilitating the understanding of the disclosure, anddo not limit the present disclosure unless otherwise noted. Elementshaving substantially the same functions and configurations herein and inthe drawings are denoted by the same reference symbols to omit redundantdescription thereof. Further, illustration of elements with no directrelationship to the present disclosure is omitted.

A method of producing a silicon compound material and an apparatus forproducing a silicon compound material according to an embodiment of thepresent disclosure are hereinafter described in detail with reference tothe drawings. In this embodiment, as the silicon compound material, theproduction of a silicon carbide-based ceramic matrix composite usingsilicon carbide for both a preform and a matrix is supposed.

Design of By-Product Decreasing Reaction

A by-product generation reaction mechanism is analyzed through use of areaction mechanism based on quantum chemical calculation, and reactionconditions for decreasing the generation amount of a by-product anderadicating the by-product are considered.

It is considered that a precursor of a by-product generated from a mixedgas of methyltrichlorosilane and a hydrogen gas (hereinafter sometimesdescribed as “MTS/H₂”) is SiCl₂, and the by-product is generated throughpolymerization of SiCl₂ (see Non Patent Literature 1). There is noexample of making a detailed investigation into the molecular weight,the structure, and the like of the by-product in a MTS/H₂ system, but adetailed investigation has been made into a system of a mixed gas oftrichlorosilane and a hydrogen gas (hereinafter sometimes described as“SiHCl₃/H₂”) (see Non Patent Literature 2). It has been reported that aby-product in the SiHCl₃/H₂ mixed gas system includes Si_(n)Cl_(2n+2)and (SiCl₂)_(n) (n=3 to 6). It is anticipated that, in the by-product inthe MTS/H₂ mixed gas system, in which SiCl₂ is generated as in theSiHCl₃/H₂ system, Si_(n)Cl_(2n+2) or (SiCl₂)_(n) is generated in thesame manner. In view of the foregoing, as illustrated in FIG. 2, a(SiCl₂)_(n) system is considered in this embodiment.

The following three methods of decreasing the generation of a by-productas illustrated FIG. 3 to FIG. 5 are obtained in this embodiment. Thedetails thereof are described further below.

1) As illustrated in FIG. 3, an exhaust gas is retained at about 600° C.(500° C. or more and less than 950° C.) in a reforming furnace.2) As illustrated in FIG. 4, at least any one of N₂, H₂, HCl, CH₃Cl,CCl₄, C₂HCl₃, C₂H₃Cl₃, C₂H₄ , C₂H₆O, C₃H₆O, CH₄O, H₂O, CH₂Cl₂, or CHCl₃is added to an outlet of a reaction furnace.3) As illustrated in FIG. 5, at least any one of N₂, H₂, HCl, CH₃Cl,CCl₄, C₂HCl₃, C₂H₃Cl₃, C₂H₄, C₂H₆O, C₃H₆O, CH₄O, H₂O, CH₂Cl₂, or CHCl₃is added, and an exhaust gas is retained at 200° C. or more and lessthan 1,100° C. in a reforming furnace.

Construction of By-Product Generation Reaction Mechanism

Although Si_(n)Cl_(2n+2) and (SiCl₂)_(n) have been consideredproblematic for years, there are no thermodynamic data of the by-productand no data on the generation reaction rate etc. of the by-product. Thethermodynamic data of Si_(n)Cl_(2n+2) and (SiCl₂)_(n) (n≥13) and theirgeneration reaction rate constants were calculated through quantumchemical calculation. A molecular structure, an energy, and a frequencywere calculated through use of Gaussian 09D (see Non Patent Literature3) at the CBS-QB3//B3LYP/CBSB7 level. The reaction rate constants werecalculated through use of GPOP (see Non Patent Literature 4) and SSUMSE(see Non Patent Literature 5).

A change in free energy through polymerization of SiCl₂ is shown in eachof FIG. 6A and FIG. 6B. In linear polymerization cases shown in FIG. 6A,SiCl₂ in an unbound state has a lower free energy and is more stable at1,100 K or more, and SiCl₂ in a polymerized state has a lower freeenergy and becomes gradually stable at 1,100 K or less. Meanwhile, incyclic polymerization cases shown in FIG. 6B, SiCl₂ has the highest freeenergy and is most unstable at a certain polymerization degree, and hasa lower free energy and becomes more stable with an increase inpolymerization degree. The polymerization degree and free energy atwhich SiCl₂ is most unstable vary with temperature.

A reaction energy and a reaction barrier of a reaction between SiCl₂ andanother molecule at 0 K are illustrated in FIG. 7 (see Non PatentLiteratures 1 and 2). When the case in which SiCl₂ follows a right sidepath of FIG. 7 in which SiCl₂ reacts with another SiCl₂ to become Si₂Cl₄(Cl₂SiSiCl₂, Cl₃SiSiCl) and the cases in which SiCl₂ follows left sidepaths of FIG. 7 in which SiCl₂ reacts with H₂, HCl, and the like arecompared to one another, a product of the reaction between SiCl₂ withanother SiCl₂ has a higher energy and is more unstable than any ofproducts of the reactions on the left side. However, when reactionbarriers between SiCl₂ and those products are compared to one another,whereas all the products on the left side excluding the product in thecase of butadiene have a barrier of 50 kJ/mol or more, a barrier toSi₂Cl₄ is low with respect to original SiCl₂ and is lower than thebarriers to the products on the left side.

From the above-mentioned results, when the temperature of SiCl₂, whichis stable at high temperature, is reduced from 1,000° C. or more andretained at a certain temperature, SiCl₂ primarily becomes Si₂Cl₄, whichhas a low reaction barrier. However, Si₂Cl₄ in itself is unstable ascompared to SiHCl₃ or SiH₂Cl₂, and hence a reaction in which Si₂Cl₄becomes SiHCl₃ or SiH₂Cl₂ over time is anticipated.

A reaction path from SiCl₂ to (SiCl₂)₃ at 0 K is illustrated in FIG. 8.Each product in the path from SiCl₂ to (SiCl₂)₃ has a low energy and alow reaction barrier with respect to SiCl₂, and hence it is anticipatedthat SiCl₂ becomes (SiCl₂)₃ significantly easily at 0 K. Based on thoseenergy paths, the reaction rate constant of a SiCl₂ polymerizationreaction was calculated.

Feature Prediction of By-Product Generation Reaction

The above-mentioned reaction mechanism was introduced into a MTS/H₂reaction mechanism. Reaction calculation was performed through use ofthe reaction mechanism and CHEMKIN (see Non Patent Literature 6). Inorder to grasp the feature of SiCl₂, first, a SiHCl₃/H₂ mixed gas wasconsidered. As a temperature distribution, a temperature distribution asshown in the upper part of FIG. 9 was used. The temperature distributionis made with reference to a gold furnace actually used as a reactionfurnace, and a temperature is drastically reduced on an outlet side.Reaction calculation was performed under the conditions in which theSiHCl₃/H₂ mixed gas flows as a plug flow in a cylindrical tube having aninner diameter of 16 mm under gas conditions of a partial pressure ratiobetween SiHCl₃ and H₂ of 1:37 (under reduced pressure) and a flow rateof 1.08 slm.

A change in gas mole fraction is shown in the lower part of FIG. 9. Asshown in FIG. 9, it was anticipated that a higher-chlorosilane(SiCl₂)_(n), which was considered as one by-product, was generated inthe course of temperature reduction, not in a soaking region of about900° C. in a CVI reaction furnace. With this, it is anticipated that thegeneration temperature of a by-product is lower than 600° C. Anillustration of a bomb of FIG. 9 indicates that the higher-chlorosilanemay become an explosive substance when oxidized in contact with theatmosphere. The same applies hereinafter.

A main reaction of SiCl₂ occurring at from 400° C. to 800° C. in thecourse of temperature reduction in FIG. 9 is illustrated in each of FIG.10A, FIG. 10B, and FIG. 10C. At the temperatures, the following reactionproceeds (see Non Patent Literature 1).

Linear Si_(n)Cl_(2n+2)→SiCl₄+(n−1)SiCl₂

At 800° C. illustrated in FIG. 10A, polymerization does not occur and amonomolecule having single Si is generated. When a temperature reachesdown to 600° C. illustrated in FIG. 10B, a linear SiCl compound isgenerated. When the temperature reaches down to 400° C. illustrated inFIG. 10C, a cyclic compound is generated.

It is said as an experimental rule that, in CVD using SiHCl₃/H₂, theamount of the by-product is decreased by warming an exhaust pipe.Therefore, calculation in which the temperature of a thermallydecomposed SiHCl₃/H₂ gas was retained on a downstream side wasperformed. FIG. 11A and FIG. 11B correspond to an example in which thetemperature is retained at 800° C. A configuration on the downstreamside is illustrated in FIG. 11A, in which a reforming furnace forpost-treatment is arranged in a stage subsequent to a reaction furnace.A temperature distribution and the contents of higher-chlorosilanes areshown in FIG. 11B.

The results of reaction calculation in the case of changing theretention temperature to 800° C., 600° C., and 400° C. are shown in FIG.12A, FIG. 12B, and FIG. 12C, respectively. FIG. 12A, FIG. 12B, and FIG.12C each correspond to a post-treatment part of FIG. 11A and FIG. 11B.At 800° C. shown in FIG. 12A, SiCl₂ is stable because of the hightemperature, and hence SiCl₂ does not react but finally becomes theby-product when cooled. In contrast, at 400° C. shown in FIG. 12C, theby-product is stable because of the low temperature, and hence SiCl₂becomes the by-product. At 600° C. shown in FIG. 12B, SiHCl₃ isgenerated through the following reaction presumably because both SiCl₂and the by-product are unstable and SiHCl₃ is stable.

SiCl₂+HCl→SiHCl₃

From the above-mentioned results, it is anticipated that a temperaturearound 600° C. is suitable for converting SiCl₂ into SiHCl₃, which isenergetically stable.

Design of By-Product Decreasing Reaction Without Addition of Gas

In order to consider SiCl₂ decreasing conditions for a MTS/H₂ gas,reaction calculation was performed in the same manner. The conditions ofthe calculation were as follows: a partial pressure ratio among MTS, H₂,and He of 2:5:18 (under reduced pressure); an inner diameter of 16 mm;and a total flow rate of 100 sccm. The result at the time of directlyreducing a temperature is shown in FIG. 13. It is considered that thehigher-chlorosilanes are generated as in the SiHCl₃/H₂ system.

It is supposed that the residual amount of SiCl₂ is directly linked tothe generation amounts of the higher-chlorosilanes, and hence only theresidual rate of SiCl₂ is considered. A change in residual rate of SiCl₂at the time of changing a retention temperature of an exhaust gas in arange of from 500° C. to 750° C. is shown in FIG. 14. When the exhaustgas is retained at a temperature of from 700° C. to 750° C., adiminution speed of SiCl₂ is high, but SiCl₂ remains in a larger amount.Meanwhile, when the exhaust gas is retained at a temperature of lessthan 600° C. and subjected to a reaction for a sufficient time period,the residual rate is considerably decreased, but the diminution speedbecomes lower. For example, whereas SiCl₂ is decreased fastest throughtreatment at 700° C. at a residual rate of SiCl₂ of about 10%, SiCl₂ isdecreased fastest through treatment at 650° C. at a residual rate ofSiCl₂ of about 1%. Therefore, it is considered that, when the treatmenttemperature of SiCl₂ is gradually reduced from 700° C. or more, atreatment time period is shortened and the volume of a reforming furnacerequired for the treatment is decreased, as compared to the case ofkeeping the temperature constant.

In FIG. 14, the diminution speed of SiCl₂ at each temperature is definedby the following equation.

dC/dt=−k _(SiCl2) ×C   (1)

In the equation, C represents the concentration of SiCl₂, and trepresents a residence time (sec). FIG. 15 is a graph for showing acurve obtained by plotting a residual rate (%) of SiCl₂, C/C₀, on theabscissa and kSiCl₂ on the ordinate at various temperatures. As seenfrom FIG. 15, for example, when the residual rate of SiCl₂ is 15% ormore, the maximum kSiCl₂ is obtained through retention at 750° C., butwhen the residual rate of SiCl₂ is between 9% and 15%, the maximumkSiCl₂ is obtained through retention at 700° C. In this way, it isanticipated that a temperature at which the maximum kSiCl₂ is obtainedis reduced with a decrease in residual rate of SiCl₂.

Accordingly, when the temperature of the exhaust gas is controlled sothat the maximum rate constant kSiCl₂ is obtained in accordance with theresidual rate of SiCl₂, the residual rate of SiCl₂ can be decreasedfastest, and by extension, also the generation of a liquid by-productcan be decreased. In other words, when the temperature of the exhaustgas is controlled and reduced at a predetermined rate to subject theexhaust gas to continuous thermal history, the diminution speed of theresidual rate of SiCl₂ can be increased. For this, the temperature ofthe exhaust gas is controlled as follows: the temperature of the exhaustgas is gradually and continuously reduced from 700° C. so that acontinuous temperature reduction curve is obtained. It is alsoappropriate to adopt a temperature reduction curve on which thetemperature of the exhaust gas is appropriately reduced to a pluralityof discrete temperatures in a stepwise manner. In addition, the liquidby-product sometimes becomes a solid when the by-product is brought intocontact with another substance (e.g., oxygen) in an environment. Theliquid or solid by-product is hereinafter sometimes referred to simplyas “by-product”.

A line of FIG. 15 is obtained by following the maximum kSiCl₂'s at therespective residual rates of SiCl₂. At this time, the followingrelational equation is established between kSiCl₂ and C/C₀.

k _(SiCl2)=6.1×(C/C₀)^(0.29) s⁻¹  (2)

As is apparent from FIG. 15, the temperature at which the maximum kSiCl₂is obtained varies depending on the residual rate. A plot of the maximumkSiCl₂ vs. the reciprocal (1000/T) of the temperature T on the abscissais shown in FIG. 16. From FIG. 16, the following relational equation canbe established between the maximum kSiCl₂ and T.

k _(SiCl2)=2.0×10⁴×exp(−70 kJ/mol/RT)  (3)

R represents a gas constant of 8.314 J/mol/K.

When the equation (2) is plugged in the equation (1), the followingequation is obtained.

$\frac{dC}{dt} = {{{{- 6.1} \times \frac{C^{1.29}}{C_{0}^{0.29}}}\therefore\frac{dC}{C^{1.29}}} = {{- 6.1} \times C_{0}^{0.29}{dt}}}$

When the both sides are integrated, the following equation is obtained.

$\left( \frac{C}{C_{0}} \right)^{- 0.29} = {{0.29 \times 6.1 \times t} + {A\mspace{14mu} \left( {A\mspace{14mu} {is}\mspace{14mu} a\mspace{14mu} {{constant}.}} \right)}}$

A represents 1 because C/C₀ becomes closer to 1 when t becomes closer to0, and hence the following equation (4) is obtained.

$\begin{matrix}{\frac{C}{C_{0}} = \left( {{1.8t} + 1} \right)^{- \frac{1}{0.29}}} & (4)\end{matrix}$

When the equation (4) is plugged in the equation (2), and the resultantis compared to the equation (3), the following equation is obtained.

$\begin{matrix}{k_{{SiCl}\; 2} = {\frac{6.1}{{1.8t} + 1} = {{{2.0 \times 10^{4} \times {\exp \left( {- \frac{70\mspace{14mu} {kJ}\text{/}{mol}}{RT}} \right)}}\therefore{- \frac{70\mspace{14mu} {kJ}\text{/}{mol}}{RT}}} = {{{\ln \left( \frac{6.1}{\left( {{1.8t} + 1} \right) \times 2.0 \times 10^{4}} \right)}\therefore T} = {\frac{8.4 \times 10^{4}}{{\ln \left( {{1.8t} + 1} \right)} + 8.1}\mspace{14mu} (K)}}}}} & (5)\end{matrix}$

The equation (5) represents a temporal change in temperature of theexhaust gas for achieving the maximum kSiCl₂. When the temperature ofthe exhaust gas is changed so as to follow the equation (5), it isconsidered that the residual rate C/C₀ of SiCl₂ is decreased inaccordance with the equation (4). While it is considered that thenumerals in the equations (4) and (5) change depending on the conditionsof the exhaust gas, when each parameter in the equation (5) isdetermined by the procedure performed in this section, it is consideredthat a temperature reduction method optimal to the conditions is found.

First Design of By-Product Decreasing Reaction with Addition of Gas

It was considered whether SiCl₂ was decreased by adding another gas toan exhaust gas. He, H₂, HCl, and CH₃Cl were considered. In addition,CH₂Cl₂, and CHCl₃ and CCl₄, which were expected to have similar effects,were considered. The conditions of calculation are as illustrated inFIG. 17.

The result of comparison of the residual rates of SiCl₂ in a 600° C.region described above is shown in each of FIG. 18 and FIG. 19. Thecomparison between the case of not adding a gas and the cases of addingH₂, He, HCl, and CH₃Cl in addition amounts of 72 sccm is shown in FIG.18. In FIG. 18, the comparison is evaluated with a residence timexanactual flow rate on the abscissa. The comparison among the cases ofadding CH₃Cl, CH₂Cl₂, CHCl₃, and CCl₄ in addition amounts of 22 sccm isshown in FIG. 19. In FIG. 19, the comparison is performed with aresidence time on the abscissa because all the cases have the same flowrate. In each of FIG. 18 and FIG. 19, the result is that the highestdiminution speed of SiCl₂ is obtained in the case of adding CH₃Cl. He,H₂, and HCl less contribute to a reaction, and contrarily increase atotal flow rate, resulting in the necessity for an additional volume.The same applies to CH₂Cl₂, but it is anticipated that CHCl₃, CCl₄, andthe like contribute to the reaction.

A main reaction of SiCl₂ at the time of adding CH₃Cl was analyzed, andthe result of calculation was that SiCl₂ was decreased through thefollowing radical chain reactions.

SiCl₂+CH₃SiCl₂  (R1)

CH₃SiCl₂+CH₃Cl→CH₃SiCl₃+CH₃  (R2)

It is considered that SiCl₂ can be converted into CH₃SiCl₃ in the caseof adding CH₃Cl in the 600° C. region. While a CVI process using MTS/H₂is said to have a low raw material yield, there is a possibility that aprocess having a somewhat higher yield can be obtained by allowing CH₃Cland SiCl₂ to react with each other to return SiCl₂ to CH₃SiCl₃ andcollecting CH₃SiCl₃. The same applies to the case of adding CH₂Cl₂.

Next, the result of calculation in the case of adding a CH_(4−n)Cl_(n)gas at 900° C. is shown in FIG. 20. At this time, when n is increased byone, a reaction rate is increased by from 10 times or more to 100 timesor more. At this time, SiCl₂ is decreased mainly by the followingreaction.

CH_(4−n)Cl_(n)→CH_(4−n)Cl_(n−1)+Cl  (R3)

SiCl₂+2Cl→SiCl₃+Cl→SiCl₄  (R4)

It is considered that a rate at which CH_(4−n)Cl_(n) releases a Clradical bears a proportional relationship to a rate at which SiCl₂ isdecreased.

As shown in FIG. 21, according to Yang Soo Won (see Non PatentLiterature 7), the order of stability of those chloromethanes is asdescribed below.

CH₃Cl>CH₂Cl₂>CHCl₃>═CCl₄

It is considered that the above-mentioned result of calculation isobtained because CCl₄, which is the most unstable, releases a radialfastest.

At the time of adding CH₂Cl₂, a change in partial pressure of gasspecies including other gases is shown in FIG. 22. The partial pressureof CH₂Cl₂ is reduced to 1% or less of the original partial pressure inabout 0.6 second, and the partial pressure of C₂H₂ is increasedaccordingly. It is anticipated that redundant Cl to be generated at thistime reacts with SiCl₂ or H₂ to generate SiCl₄ or HCl.

Consideration was made on refinement of optimal conditions in the caseof CH₃Cl, which has a possibility of enabling recycling of MTS through areaction at 600° C. First, with regard to a CH₃Cl loading temperature,it is considered that CH₃Cl is desirably added when the temperature ofthe exhaust gas is about 600° C. because CH₃Cl is thermally decomposedat 750° C. or more, though CH₃Cl is stable as compared to otherCH_(4−n)Cl_(n)'s as shown in FIG. 21.

The result of calculation at the time of changing the flow rate of CH₃Clis shown in FIG. 23. When the flow rate is increased from 7 sccm to 22sccm, a diminution speed is increased according to an increase inpartial pressure of CH₃Cl, and a gas volume required for a reaction isdecreased. However, when the flow rate is increased from 22 sccm to 72sccm, the gas volume required for the reaction is increased contrarilyowing to the increase in the flow rate. This indicates the existence ofa flow rate optimal to the original exhaust gas, and it is anticipatedthat the optimal flow rate is probably comparable to the flow rate ofthe exhaust gas.

The result at the time of changing a temperature while fixing the flowrate of CH₃Cl to 22 sccm is shown in FIG. 24. A reaction rate isgenerally increased with an increase in temperature, and hence it isanticipated that the diminution speed of SiCl₂ is increased with anincrease in temperature. However, in the result of calculation, adecomposition speed is decreased with an increase in temperature.

A possible cause for this is that, as shown by the reactions (R1) and(R2), reactions between CH₃Cl and SiCl₂ are chain reactions through aCH₃ radical. Main reactions through a CH₃ radical at 600° C. and 700° C.are illustrated in FIG. 25A and FIG. 25B, respectively. A leftward bargraph represents consumption of CH₃ through the reaction, and arightward bar graph represents generation of CH₃ through the reaction.As seen from FIG. 25A, a CH₃ radical reacts almost exclusively withSiCl₂ at 600° C. However, the CH₃ radical reacts with HCl, H₂, CH₃SiCl₃,and the like at 700° C. A larger amount of CH₃ is consumed by reactionswith other molecules at a higher temperature, and CH₃ cannot contributeto the reaction with SiCl₂. Accordingly, it is considered that a mixedgas of the exhaust gas and CH₃Cl is desirably retained at about 500° C.or more and about 600° C. or less.

Summary

Possible methods of decreasing the generation of the by-product based onthe above-mentioned results, and expected advantages and disadvantagesthereof are as described below.

1) In the case of not adding a gas, a temperature is retained at about600° C. or reduced gradually from about 700° C. This method has thefollowing advantage as compared to other methods: the method is free ofcost of an additive gas because there is no need to consider theaddition of the gas. However, a reaction rate is lower than those inother cases of adding the gas, and hence a reforming furnace configuredto perform treatment at from 600° C. to 700° C. is arranged (see FIG.3).

2) In the case of adding CH₂Cl₂, CHCl₃, or CCl₄, a reaction is completedin from 1/1000 second to 0.1 second, and hence it may be considered thatthe reaction is desirably performed with residual heat of a reactionfurnace by arranging an additive gas introduction port at an outlet ofthe reaction furnace. It is considered that SiCl₂ can be sufficientlydepleted with the residual heat for a time period in the course from theadditive gas introduction port to an exhaust port, and hence it isanticipated that lower apparatus cost and lower power consumption areobtained as compared to the case of further arranging a reformingfurnace configured to retain a temperature at an outside of the reactionfurnace. However, this method involves cost of an additive gas, unlikethe case of not adding a gas. In addition, as shown in FIG. 20, sootresulting from C₂H₂ and a carbon chloride compound, such asC_(x)H_(y)Cl_(z), e.g., a vinyl chloride monomer (C₂H₃Cl) are generatedin accordance with the loading amount of CH_(4−n)Cl_(n), and occurrenceof a significantly chaotic reaction is anticipated. It is anticipatedthat a load on an exhaust gas treatment device is increased accordingly.

3) In the case of adding CH₃Cl and retaining a temperature at from 500°C. to 600° C. in a reforming furnace, treatment can be completed in ashort time period as compared to the case of not adding a gas. Besides,SiCl₂ is converted into MTS. In addition, from FIG. 22, it is consideredthat CH₃Cl is not decomposed at 600° C. or less and nearly 99% thereofremains unlike the situation of the item 2), and hence it is consideredthat little soot is accumulated.

In this embodiment, the method of decreasing the generation of theby-product has been considered with a focus on SiCl₂. The thermodynamicconstant and reaction rate constant of SiCl₂ were calculated based onquantum chemical calculation. As a result, it was presumed that theby-product was generated mainly at 500° C. or less, and the threeexamples of the method of decreasing the generation of SiCl₂ at from500° C. to 600° C. or more were given.

In this embodiment, calculation was performed on a (SiCl₂)_(n)generation reaction mechanism in which n is up to 3, and hence actual(SiCl₂)_(n) generation behavior may differ from the result of thecalculation. Therefore, precision may be further increased so that amethod of decreasing the generation of the by-product using conditionsat a boundary at which the by-product is barely generated is predicted.For example, a reaction mechanism in which n is 4 or more may beconstructed.

In addition, a by-product in which Si—C is mixed is also considered. Thereaction energies between SiCl₂ and C-based molecules are calculated,and the results thereof are shown in FIG. 26, FIG. 27A, and FIG. 27B. Ineach of FIG. 27A and FIG. 27B, a zero-point energy (bold characters) anda free energy (KJ/mol) at 1,300 K are compared. SiCl₂ is decreased inenergy and stabilized through any reaction with a C-based chemicalspecies (MTS, C₂H₄, C₂H₂, or t−1, 3-C₄H₆), and hence has a possibilityof reacting with these molecules. Of those, reactions between dienes andSiCl₂ have been reported also in a previous literature (see Non PatentLiterature 8), and it is anticipated that SiCl₂ reacts with dienessignificantly easily because of low reaction barriers.

It has been reported that a large number of Si—C bonds are present inthe by-product, and hence a cyclic (CH₂SiCl₂)_(n) structure and a changein energy are considered. Structures in which n is 2, 3, and 4 areillustrated in FIG. 28A, FIG. 28B, and FIG. 28C, respectively. Withreference to a change in energy shown in each of FIG. 29A and FIG. 29B,the energy of cyclic (CH₂SiCl₂)_(n) is decreased with an increase inpolymerization degree, and it is anticipated that cyclic (CH₂SiCl₂)_(n)is most stable when n is 3. A reaction mechanism in which such moleculeis generated in the by-product in which Si—C is mixed may beconstructed.

EXAMPLE 1

As Example 1 to which this embodiment is applied, an experiment in thecase of arranging a reforming furnace configured to retain a gasdischarged from a reaction furnace at a predetermined temperature wasperformed.

The configuration of the experiment is illustrated in FIG. 30. In astage subsequent to the reaction furnace, the reforming furnace havingthe same volume is arranged. The reforming furnace was of a hot walltype. In a stage subsequent to the reforming furnace, a quadrupole massspectrometer (QMS) for gas analysis, a cold trap configured to collect aby-product at room temperature, and a vacuum pump by means of a rotarypump (RP) were arranged. With such configuration, the experiment wasperformed by changing the temperature of the reforming furnace from 300°C. to 950° C., and a temperature of the reforming furnace at which theby-product showed the largest decrease was considered.

A raw material gas to be used in a test had a flow rate ratio ofMTS:H₂:He=1:1:0.05. A reaction furnace formed of a quartz tube was used.The reaction furnace had dimensions measuring 60 mm in inner diameterand 2,100 mm in length, and its heating region is separated into sixzones (350 mm per zone). Three zones on an upstream side were used asthe reaction furnace, and three zones on a downstream side were used asthe reforming furnace.

A relationship between the by-product collected and a treatmenttemperature in the reforming furnace is shown in FIG. 31. The yield ofthe by-product when the amount of substance (mole number) of MTS to besupplied is defined as 100% is shown. The case of a treatmenttemperature in the reforming furnace of 300° C., in which the rawmaterial gas was not decomposed and no by-product was generated, wasregarded as “without treatment”. In addition, a value compared to theamount of the by-product at this time was used as a decrease amount ofthe by-product at a treatment temperature of from 600° C. to 800° C.

As seen from FIG. 31, when the treatment temperature in the reformingfurnace was from 600° C. to 800° C., the result was that the by-productwas decreased with an increase in treatment temperature. At 950° C., SiCis generated, and hence the amount of substance to be used for formationof a SiC film is large as compared to the cases at other temperatures.Therefore, the amount of the by-product is smaller than that in the caseof 300° C. regarded as “without treatment”. For example, also in a rangeof from 500° C. to 950° C., the by-product is observed to be decreased.

In each of the case of not arranging a reforming furnace and the case ofarranging a reforming furnace configured to retain a temperature at 600°C., a liquid obtained by collecting an exhaust gas other than theby-product at low temperature was subjected to gas chromatography massspectroscopy (GC/MS) in a stage subsequent to the reforming furnace, andthe result thereof is shown in Table 1. A detected gas was representedby the symbol “o”. The number of kinds of gases was increased in thecase of arranging the reforming furnace at 600° C., and hence it wasconfirmed that SiCl₂ serving as a precursor of the by-product wasconverted into other gases.

TABLE 1 With Without reforming Component reforming furnace name furnace600° C. HCl ○ ○ SiCl₄ ○ ○ CH₃SiCl₃ ○ ○ (raw material) SiHCl₃ ○ ○C₂H₃SiCl₃ ○ ○ C₂H₅SiCl₃ ○ ○ C₂H₅Cl ○ CH₃SiHCl₂ ○ C₂H₃SiHCl₂ ○ Si₂Cl₆ ○

In addition, a content concentration of MTS in the collected liquid wasshown in FIG. 32. The concentration of MTS was increased by 1.7 times inthe case of arranging the reforming furnace at 600° C., and hence it wasconfirmed that SiCl₂ was converted into MTS.

The residence time of a MTS gas in the reforming furnace is about 1.5seconds. When the reforming furnace is set so as to have a temperaturegradient in temperature regions of the three zones from the upstreamside (800° C., 700° C., and 600° C. from the upstream side), theresidence time of the MTS gas in each zone is about 0.5 second. Theyield of the by-product with respect to the loading amount of MTS in thecase of the temperature gradient was 7.2%.

Consideration has been made on decrease of the generation of theby-product by arranging the reforming furnace in a stage subsequent tothe reaction furnace. The generation of the by-product was decreasedwhen the temperature of the reforming furnace fell within apredetermined range. In addition, it was confirmed that the precursor ofthe by-product was converted into MTS.

EXAMPLE 2

As Example 2 to which this embodiment is applied, an experiment wasperformed on a by-product difference in the case in which a reformingfurnace has high temperature.

The configuration of the experiment is illustrated in FIG. 33. Thereforming furnace is arranged in a stage subsequent to a reactionfurnace. A MTS/H₂ mixed gas is supplied to the reaction furnace. Thereforming furnace is retained at from 600° C. to 1,500° C. An effect wasanalyzed by arranging a cold trap retained at −80° C. in a stagesubsequent to the reforming furnace.

In the cold trap, an exhaust gas component discharged from the reformingfurnace was condensed and was then returned to room temperature, and agasified component (raw material gas or the like) was evaporated. Aresidue thus obtained after the evaporation of the gasified componentwas evaluated as a liquid by-product having the possibility of adheringto a pipe at room temperature.

An appearance photograph of the liquid by-product obtained under thetemperature conditions of the reforming furnace and an appearancephotograph of the by-product stabilized into silica through hydrolysisare shown in FIG. 34. The measurement result of the weight of silicaafter the stabilization, and a raw material loading ratio obtained bydividing a mole number of silica by a total mole number of MTS loaded ina CVI step are shown in Table 2.

TABLE 2 Temperature of Raw reforming Weight material furnace of silicaloading (° C.) (g) ratio (%) None (15) (5) 600 (3)  (1) 750 30 10 1,40026 9 1,500 8 3

According to Table 2, under the conditions in which the temperature ofthe reforming furnace was 1,500° C., the amount of the liquid by-productwas able to be decreased to half as compared to the case of notarranging the reforming furnace. Meanwhile, under the conditions inwhich the temperature of the reforming furnace was 750° C. or 1,400° C.,the amount of the liquid by-product was doubled, and an adverse effectwas obtained.

A possible cause for this is as described below. Unreacted MTSdischarged from the reaction furnace is decomposed in the reformingfurnace, and is precipitated as SiC. However, there is a temperatureregion in which a ratio of the unreacted MTS decomposed as SiCl₂ servingas a precursor of the by-product exceeds a ratio of the unreacted MTSprecipitated as SiC. It is considered that the temperatures of 750° C.and 1,400° C. are included in the region, and the temperature of 1,500°C. having a high reaction rate for SiC formation is beyond the region. Aby-product difference depending on the temperature of the reformingfurnace based on a model assuming such a mechanism is illustrated inFIG. 35. Therefore, as a method of consuming SiCl₂ serving as aprecursor of the by-product, also a method involving precipitating SiCl₂as a SiC-form solid substance at 1,500° C. or more is one effectivemethod.

It is considered that, when the reforming furnace has a temperaturefalling within a predetermined range including 750° C. and 1,400° C.,the ratio of the unreacted MTS decomposed as SiCl₂ serving as aprecursor of the by-product exceeds the ratio of the unreacted MTSdecomposed and precipitated as SiC in the reforming furnace, whichcontributes to an increase in amount of the liquid by-product.

EXAMPLE 3

As Example 3 to which this embodiment is applied, an experiment in thecase of adding N₂, HCl, or CH₂Cl₂ and performing treatment in areforming furnace was performed.

FIG. 36 is a conceptual view of exhaust gas treatment with an additivegas. The reforming furnace was arranged in a stage subsequent to areaction furnace, and the additive gas was supplied from an inlet of thereforming furnace. The additive gas is preferably a chlorine-based gascontaining chlorine. In the reforming furnace, a mixed gas of a gasdischarged from the reaction furnace and the additive gas is subjectedto treatment at a predetermined temperature of from 200° C. to 1,100° C.The additive gas is not limited to CH₂Cl₂, CHCl₃, CCl₄, and CH₃Cldescribed above, and may include N₂, H₂, HCl, an alcohol (ethanol,acetone, or methanol), and water vapor. The alcohol or water vapor isknown to vigorously react with a by-product at room temperature, andhence may be added at room temperature. In addition, the additive gasmay be added so that the amount of substance of the additive gas islarger than the amount of substance of a liquid or solid by-product.

The configuration of the experiment is illustrated in FIG. 37. Anelectric furnace used in this experiment is a six-zone electric furnacein which six electric furnaces are continuously connected to oneanother. A temperature can be set in each zone. Each electric furnacehas a length of 350 mm and an inner diameter of φ60 mm. Of those zones,the first five zones served as a reaction region corresponding to thereaction furnace, and the last one zone served as a reforming regioncorresponding to the reforming furnace.

The electric furnace has a reaction tube which is formed of a quartzcircular tube and is of a hot wall type in which the entirety of thetube is heated. A MTS/H₂/He mixed gas was used as a raw material. He isa standard gas for standardization of gas analysis based on a quadrupolemass spectrometer (QMS). QMS was mounted to an exhaust pipe in thevicinity of the reaction tube. The gas analysis based on QMS wasperformed for determination of the residual rate of a MTS gas and forqualitative analysis of gases to be generated through thermaldecomposition of the MTS/H₂ mixed gas.

The by-product is collected with a trap pipe mounted to the exhaustpipe, and based on the weight thereof, the generation rate of theby-product is discussed. The additive gas was added from the middle of aNo. 6 electric furnace (near the center of the circular tube of thereaction furnace, and at a distance of 175 mm from an edge of the No. 6electric furnace), which is on the most downstream side of the six zonesof FIG. 37. The introduction direction of the additive gas is anupstream direction. In Example 3, an increase or decrease of theby-product depending on the additive gas was to be evaluated, and hencea mass balance was determined for gases and a film to be generated fromMTS serving as a raw material through a reaction. The mass balance wasdetermined on the following assumption when the amount of substance(mole number) of MTS (CH₃SiCl₃) to be supplied was defined as 100%.

1) The amount of a SiC film to be formed was experimentally determined.

-   The amount of a SiC film to be formed was a total value of the    amounts of substance of SiC films to be formed on the quartz tube, a    Si substrate, and felt, but for simplicity, the yield of the SiC    film in each case was assumed to be the same as a single    experimental value (12%).    2) The residual rate of MTS was experimentally determined.-   In the QMS gas analysis, a QMS signal intensity at room temperature    was assumed to be 100%, and the residual rate of MTS was calculated    based on a ratio between the QMS signal intensity at room    temperature and a signal intensity at the time of thermal    decomposition at high temperature.    3) The amount of the by-product was experimentally determined.-   A by-product collecting pipe mounted to the exhaust pipe was used to    quantitatively analyze the amount of substance of the by-product    based on the weight of collected matter.-   At the time of calculation, the amount of substance of the    by-product was determined on the assumption that the by-product was    SiCl₂ (molecular weight: 98.5 g/mol).    4) The amounts of substance of other gasses were calculated as a    residue obtained by subtracting the above-mentioned items 1), 2),    and 3) from 100.-   The gas species generated were also evaluated through qualitative    evaluation based on QMS.

In Example 3, four experimental conditions of “without an additive gas”,“N₂ addition”, “HCl addition”, and “CH₂Cl₂ addition” are compared, andthe conditions are shown in Table 3. The mixed gas used in Example 3 hada flow rate ratio of MTS:H₂:He=1:1:0.05, and the additive gases wereadded in the same amount.

TABLE 3 Without With additive Item additive gas gas Flow rate of(Arbitrary 0.00 1.00 additive gas unit) Flow rate of MTS (Arbitrary 1.00unit) Flow rate of H₂ (Arbitrary 1.00 unit) Flow rate of He (Arbitrary0.05 (QMS unit) standardization gas) Total flow rate (Arbitrary 2.053.05 unit) Temperature ° C. (Six zones have the same temperaturesetting) Total pressure Pa Reduced pressure Film formation Hour(s) 6time period

The results of the mass balance in CVI are summarized in FIG. 38. Fromthe qualitative analysis based on QMS, it was revealed that at least“CH₄, C₂H₂, C₂H₄, SiCl₄, SiHCl₂, HCl, and Cl₂” gases were generated as“other gases” to be generated through thermal decomposition of MTS.

In the case of no additive gas, the by-product is generated at ageneration rate of 9.5% in terms of mass balance. In contrast, in thecase of N₂ addition, the generation rate was decreased to 6.4%. This ispresumably because a gas flow velocity is increased through addition ofthe additive gas and the by-product is pushed to a downstream side ofthe exhaust pipe, rather than because the by-product is decreasedthrough a reaction and the like. Therefore, in an additive gas test ofExample 3, the presence or absence of an effect was compared using theresult in the case of N₂ addition as a reference. However, it is notdenied that a change in reaction mechanism through N₂ addition mayessentially have a decreasing effect on the generation of theby-product.

In the case of CH₂Cl₂ addition, the generation of the by-product was notobserved, and also other residues and the like were not generated.Comparison of the results of the gas analysis based on QMS in the casesof N₂ addition, HCl addition, and CH₂Cl₂ addition is shown in FIG. 39Aand FIG. 39B. Overall data is shown in FIG. 39A, and data near theregion A of FIG. 39A is shown in FIG. 39B in an enlarged manner.

In the case of CH₂Cl₂ addition, a gas molecule having a mass number of62 m/z, which was not observed in the cases of N₂ addition and HCladdition, was observed. If the gas molecule having a mass number of 62m/z is a molecule containing Cl, a spectrum has a feature in accordancewith the presence ratios of isotopes of Cl (35 g/mol and 37 g/mol). As aresult, it can be determined that the molecule having a mass number of62 m/z is a molecule not containing Cl. Therefore, in consideration of amolecular weight, the molecule having a mass number of 62 m/z ispresumed to be disilane (Si₂H₆). It is reasonable to consider moleculeshaving a mass number of 59 m/z, 60 m/z, and 61 m/z to be disilane(Si₂H₆) fragments, that is, molecules in each of which H is removed fromdisilane.

In the case of HCl addition, the generation rate of the by-product interms of mass balance was decreased to 2.7%. The by-product wasdecreased to half or less as compared to the case of N₂ addition (6.4%).Meanwhile, the residual rate of MTS is increased from 12% to 19%. Theresult indicates that a reaction in which a precursor of the by-productreturns to MTS is promoted through HCl addition. In addition, as shownin FIG. 39A and FIG. 39B, the generation of a particular gas moleculewas not able to be confirmed in exhaust gas analysis based on QMS in thecase of HCl addition. Based on the facts that the by-product isdecreased to half, the residual rate of MTS is increased, and a gascomposition has no particular change, it can be presumed that, throughHCl addition, a reaction in which SiCl₂ serving as a precursor of theby-product returns to MTS (CH₃SiCl₃) prevails over a reaction in whichSiCl₂ is polymerized to generate the by-product. In this case, it isconsidered that complicated reaction pathways are involved.

Disilane is a combustible gas easily burned at room temperature in airand has dangerousness, but is also a gas which has low toxicity(generally said to have no toxicity) and is generally used in thesemiconductor industry and the like, and is easily detoxified. Disilaneis highly likely to be able to be treated at least more safely than theliquid by-product precipitated in the pipe. It was revealed that amethod of decreasing the generation of the by-product through use of theadditive gas was significantly effective.

In Example 3, consideration has been made on decrease of the generationof the by-product by adding the additive gas to the gas discharged fromthe reaction furnace. It was revealed that the by-product was able to bealmost entirely vanished in the case of CH₂Cl₂ addition. In the case ofHCl addition, the by-product was decreased to half or less, and theresidual rate of MTS was increased. However, HCl entailed an increase intreatment amount of a detoxifying device owing to an increase in HClconcentration in an exhaust gas, is a gas species having a higher price,and has a low decreasing effect on the generation of the by-product ascompared to the other gases (comparable to the effect through treatmentat 600° C.)

Second Design of By-Product Decreasing Reaction with Addition of Gas

A rate constant calculation equation (6) for an elementary reactionusing SiCl₂ as a starting substance was constructed. An elementaryreaction having a higher rate constant k was presumed throughtheoretical calculation using the rate constant calculation equation(6).

$\begin{matrix}{k = {{AT}^{n}\mspace{14mu} {\exp \left( \frac{- {Ea}}{RT} \right)}}} & (6)\end{matrix}$

In the rate constant calculation equation (6), A, n, and Ea (J/mol) areconstants in each elementary reaction.

FIG. 40A is a table for showing examples of elementary reactions relatedto SiCl₂ and constants thereof. FIG. 40B is a graph for comparison ofthe rate constants of elementary reactions listed as candidates. Asshown in FIG. 40A and FIG. 40B, as a result of the theoreticalcalculation, it was predicted that SiCl₂ was able to be decreased when areaction in which any one or more of SiCl, H, HCl, and CH₃Cl weregenerated from SiCl₂ was able to be promoted through addition of anadditive gas. With this, it was presumed that, when three kinds ofgases, a HCl gas, a C_(x)H_(y)-based gas, and a C_(x)H_(y)Cl_(z)-basedgas, were each used as the additive gas, a decreasing effect on SiCl₂was exhibited.

Selection of Candidate Additive Gas

Based on the results of the “Second Design of By-product DecreasingReaction” section, out of the three kinds of gases, the HCl gas, theC_(x)H_(y)-based gas, and the C_(x)H_(y)Cl_(z)-based gas, which wereeach presumed to have a decreasing effect on SiCl₂, substances eachhaving high safety (low toxicity, low environmental load, simpledetoxifying device), easy handleability (high vapor pressure), and lowcost (widely used product, low molecular weight (g/mol)) were selected.

Specifically, six substances, HCl (hydrogen chloride), CH₃Cl(chloromethane), CH₂Cl₂ (dichloromethane), CCl₄ (tetrachloromethane,carbon tetrachloride), C₂H₃Cl₃ (trichloroethane), and C₂HCl₃(trichloroethylene), were selected as candidate additive gases.

Simulation of By-Product in the Case of Adding Additive Gas

In the same manner as in the “Feature Prediction of By-productGeneration Reaction” section, reaction calculation was performed throughuse of a MTS/H₂ reaction mechanism and CHEMKIN (see Non PatentLiterature 6). FIG. 41 is a view for illustrating simulation conditions.As illustrated in FIG. 41, the reaction calculation was performed underthe conditions in which a MTS/H₂ mixed gas (raw material gas) flows as aplug flow in a cylindrical tube having an inner diameter of 60 mm and atotal length of 2,000 mm at a flow rate ratio of MTS:H₂=1.0:0.4 underreduced pressure. In the cylindrical tube, a region ranging from an endportion (0 mm) on an upstream side in a flow direction of the rawmaterial gas to a position distant from the end portion by 1,000 mmserved as a reaction furnace, and a region ranging from the positiondistant from the end portion by 1,000 mm to a position distant therefromby 2,000 mm served as a reforming furnace. In addition, the reactioncalculation was performed given that the temperature of the reformingfurnace was set to 975° C. and an additive gas was added to thereforming furnace (corresponding to a position at a distance of 1,000 mmand a residence time t of 1.36 seconds) at a flow rate ratio ofMTS:additive gas=1.0:1.0. The reaction calculation was performed in eachof the cases of the six substances, HCl, CH₃Cl, CH₂Cl₂, CCl₄, C₂H₃Cl₃,and C₂HCl₃, as an additive gas.

FIG. 42A is a graph for showing the result of simulation in the case ofadding HCl as an additive gas. FIG. 42B is a graph for showing theresult of simulation in the case of adding CH₂Cl₂ as an additive gas.FIG. 42C is a graph for showing the result of simulation in the case ofadding CH₃Cl as an additive gas. FIG. 42D is a graph for showing theresult of simulation in the case of adding C₂HCl₃ as an additive gas.FIG. 42E is a graph for showing the result of simulation in the case ofadding C₂H₃Cl₃ as an additive gas. FIG. 42F is a graph for showing theresult of simulation in the case of adding CCl₄ as an additive gas. Ineach of FIG. 42A to FIG. 42F, the broken line represents the partialpressure of MTS, the long dashed double-dotted line represents thepartial pressure of H₂, the long dashed dotted line represents thepartial pressure of the additive gas, and the solid line represents thepartial pressure of SiCl₂.

Simulation of the by-product (SiCl₂) was performed, and the resultthereof was that the generation of SiCl₂ was suppressed by adding theadditive gas in each of the cases of HCl, CH₃Cl, CH₂Cl₂, CCl₄, C₂H₃Cl₃,and C₂HCl₃. In addition, the result was that, of those six substances,C₂HCl₃ shown in FIG. 42D had the largest decreasing effect on SiCl₂. Inaddition, the result was that CH₂Cl₂ shown in FIG. 42B, CH₃Cl shown inFIG. 42C, and C₂H₃Cl₃ shown in FIG. 42E each had a large decreasingeffect on SiCl₂.

From the above-mentioned results, it is presumed that SiCl₂ can bedecreased efficiently by adopting a C_(x)H_(y)Cl_(z)-based (0≤x+y+z≤1,0≤x, y≤1, 0<z) compound as the additive gas.

Consideration of Temperature of Reforming Furnace in the Case of AddingAdditive gas

In the same manner as in the “Simulation of By-product in the Case ofAdding Additive Gas” section, reaction calculation was performed throughuse of a MTS/H₂ reaction mechanism and CHEMKIN (see Non PatentLiterature 6). Simulation conditions are the same as in the “Simulationof By-product in the Case of Adding Additive Gas” section except for thetemperature of a reforming furnace and the total length of the reformingfurnace. The partial pressure of SiCl₂ in the cases in which thetemperature of the reforming furnace was 200° C., 400° C., 600° C., 800°C., and 1,000° C. was calculated. In addition, the reaction calculationwas performed given that each of CH₂Cl₂ and CH₃Cl was added as anadditive gas at a position having a residence time t of 1.37 seconds.

FIG. 43A, FIG. 43B, and FIG. 43C are each a graph for showing thepartial pressure of SiCl₂ in the case of adding CH₂Cl₂ as an additivegas and changing the temperature of the reforming furnace. FIG. 43A is agraph for showing a change in partial pressure of SiCl₂ depending on aresidence time at various temperatures. FIG. 43B is a graph for showingthe partial pressure of SiCl₂ at an outlet of the reforming furnace.FIG. 43C is a graph for showing a change in partial pressure of SiCl₂depending on a difference in flow rate ratio between the additive gasand MTS at various temperatures. In FIG. 43A, the solid line representsthe case of 200° C., the broken line represents the case of 400° C., thelong dashed dotted line represents the case of 600° C., the long dasheddouble-dotted line represents the case of 800° C., and the heavy linerepresents the case of 1,000° C. In addition, in FIG. 43C, the solidline represents the case of 300° C., the broken line represents the caseof 500° C., the long dashed dotted line represents the case of 700° C.,and the long dashed double-dotted line represents the case of 900° C.

As shown in FIG. 43A, the result obtained was that the decreasing effecton SiCl₂ became higher as the temperature became higher at a residencetime t of 1.68 seconds. That is, the result obtained was that thedecreasing effect on SiCl₂ became higher as the temperature becamehigher 0.31 second after the addition of CH₂Cl₂ serving as an additivegas. Meanwhile, when the residence time t exceeded 1.68 seconds, thefollowing different result was obtained: a temperature at which a higherdecreasing effect on SiCl₂ was obtained varied depending on theresidence time.

In addition, as shown in FIG. 43B, the result obtained was that thepartial pressure of SiCl₂ at the outlet of the reforming furnace waslowest when the temperature of the reforming furnace was 500° C. Inaddition, the result obtained was that the partial pressure of SiCl₂ atthe outlet of the reforming furnace was increased in an ascending orderof 500° C., 600° C., 700° C., 400° C., 800° C., 1,000° C., and 200° C.The presence of an optimal temperature range in the case of addingCH₂Cl₂ as an additive gas was theoretically revealed.

In addition, as shown in FIG. 43C, when the flow rate ratio betweenCH₂Cl₂ and MTS (CH₂Cl₂/MTS) was less than 0.7, the result obtained wasthat the decreasing effect on SiCl₂ became higher as the temperature ofthe reforming furnace became lower. In addition, when the flow rateratio was 1.6 or more, the result obtained was that the decreasingeffect on SiCl₂ became higher as the temperature of the reformingfurnace became higher. Further, when the flow rate ratio was 0.7 or moreand less than 1.6, the result was that a temperature of the reformingfurnace at which a higher decreasing effect on SiCl₂ was obtained varieddepending on the flow rate ratio.

FIG. 44A and FIG. 44B are each a graph for showing the partial pressureof SiCl₂ in the case of adding CH₃Cl as an additive gas and changing thetemperature of the reforming furnace. FIG. 44A is a graph for showing achange in partial pressure of SiCl₂ depending on a residence time atvarious temperatures. FIG. 44B is a graph for showing the partialpressure of SiCl₂ at an outlet of the reforming furnace. In FIG. 44A,the solid line represents the case of 200° C., the broken linerepresents the case of 400° C., the long dashed dotted line representsthe case of 600° C., the long dashed double-dotted line represents thecase of 800° C., and the heavy line represents the case of 1,000° C.

As shown in FIG. 44A and FIG. 44B, the result was that the partialpressure of SiCl₂ was lowest at a time point of a residence time t of1.5 seconds irrespective of the temperature of the reforming furnace.That is, the result obtained was that the partial pressure of SiCl₂ waslowest 0.1 second after the addition of CH₃Cl as an additive gas.

In addition, as shown in FIG. 44B, the result obtained was that thepartial pressure of SiCl₂ at the outlet of the reforming furnace becamelower as the temperature of the reforming furnace became lower.Specifically, the result was that the partial pressure of SiCl₂ at theoutlet of the reforming furnace was increased in an ascending order of150° C., 200° C., 400° C., 600° C., 800° C., and 1,000° C.

Consideration of Addition Amount of Additive Gas

In the same manner as in the “Consideration of Temperature of ReformingFurnace in the Case of Adding Additive Gas” section, reactioncalculation was performed through use of a MTS/H₂ reaction mechanism andCHEMKIN (see Non Patent Literature 6). Simulation conditions are thesame as in the “Consideration of Temperature of Reforming Furnace in theCase of Adding Additive Gas” section except for the addition amount ofan additive gas.

FIG. 45 is a graph for showing the partial pressure of SiCl₂ in the caseof changing the addition amount of CH₃Cl serving as an additive gas. InFIG. 45, the solid line represents the case in which the temperature ofthe reforming furnace was set to 200° C., the broken line represents thecase in which the temperature of the reforming furnace was set to 600°C., and the long dashed dotted line represents the case in which thetemperature of the reforming furnace was set to 1,000° C.

As shown in FIG. 45, the result was that the partial pressure of SiCl₂became lower as the amount of the additive gas became largerirrespective of the temperature of the reforming furnace. In addition,the result obtained was that the partial pressure of SiCl₂ wasremarkably decreased when a ratio in amount of substance between theadditive gas and MTS (additive gas/MTS) was 1 or more.

EXAMPLE 4

An experiment in which N₂, C₂H₄, HCl, CH₃Cl, CH₂Cl₂, CCl₄, C₂H₃Cl₃, orC₂HCl₃ was added as an additive gas and treatment was performed in areforming furnace was performed through use of an apparatus similar tothe apparatus of Example 3 illustrated in FIG. 37. In Example 4, zonesNos. 1 to 3 served as a reaction region corresponding to a reactionfurnace, and zones Nos. 4 to 6 served as a reforming regioncorresponding to the reforming furnace. That is, the reaction furnacehad a length of 1.05 m (350 mm×3), and the reforming furnace had alength of 1.05 m (350 mm×3). The temperature of the reforming furnacewas set to 975° C. In addition, the reaction furnace and the reformingfurnace were under reduced pressure.

In addition, a MTS/H₂/He mixed gas was supplied to the reaction furnaceas a raw material gas. The raw material gas had a flow rate ratio ofMTS:H₂:He=1.0:1.0:0.05. In addition, HCl, CH₃Cl, CH₂Cl₂, CCl₄, C₂H₃Cl₃,or C₂HCl₃ was supplied to the reforming furnace as an additive gas. Theflow rate ratio between MTS and the additive gas was as follows:MTS:additive gas=1.0:1.0.

In order to evaluate a decreasing effect on the by-product exhibited bythe additive gas, a mass balance was calculated for a SiC film and gasesto be generated from MTS contained in the raw material gas through areaction according to the kind of the additive gas. The mass balance wascalculated on the following assumption when the amount of substance(mole number) of MTS (CH₃SiCl₃) to be supplied was defined as 100%.

1) Amount of SiC Film (%)

-   The amount of a SiC film was calculated based on a total amount of    SiC films formed on a base material arranged in the reaction furnace    or the reforming furnace and on a wall surface of a quartz tube.

2) Amount of By-Product (%)

-   The amount of the by-product was calculated based on the weight of    collected matter collected in a by-product collecting tube mounted    to an exhaust pipe. The amount of the by-product was calculated on    the assumption that the by-product was SiCl₂ (molecular weight: 98.5    g/mol).

3) Amount of Unconsumed MTS (%)

-   In QMS gas analysis, a QMS signal intensity at room temperature was    assumed to be 100%, and the amount of unconsumed MTS was calculated    based on a ratio between the QMS signal intensity at room    temperature and a signal intensity at the time of thermal    decomposition at high temperature.

4) Amount of Other Gases (%)

-   The amounts of other gasses were obtained by subtracting the    above-mentioned items 1), 2), and 3) from 100%.

FIG. 46 is a graph for showing a mass balance calculated in Example 4.As shown in FIG. 46, in the case of “without an additive gas”, theby-product (SiCl₂) was generated at 13%. In addition, in the case ofadding a “nitrogen gas (N₂)” as an additive gas, the by-product wasgenerated at 16%. In the case of adding “C₂H₄ (ethylene)” as an additivegas, the by-product was generated at 6%. In addition, in the case ofadding “HCl” as an additive gas, the by-product was generated at 3%.Further, in each of the cases of adding “C₂HCl₃”, “CCl₄”, “C₂H₃Cl₃”,“CH₂Cl₂”, and “CH₃Cl” as an additive gas, no by-product was generated(0%).

From the above-mentioned results, it was confirmed that, when at leastany one substance selected from the selected six substances and C₂H₄ wasadded, the generation of SiCl₂ was able to be decreased as compared tothe case of adding a nitrogen gas at an equal gas flow rate. Inaddition, it was confirmed that the generation of SiCl₂ was able to beavoided when at least any one substance selected from “C₂HCl₃”, “CCl₄”,“C₂H₃Cl₃”, “CH₂Cl₂”, and “CH₃Cl” was added as an additive gas.

FIG. 47A to FIG. 47F are each a photograph of an exhaust pipe (a pipeconnected to the outlet of the reforming furnace) in Example 4. FIG. 47Ais a photograph in the case of not adding an additive gas. FIG. 47B is aphotograph in the case of adding HCl as an additive gas. FIG. 47C is aphotograph in the case of adding C₂HCl₃ as an additive gas. FIG. 47D isa photograph in the case of adding CCl₄ as an additive gas. FIG. 47E isa photograph in the case of adding CH₃Cl as an additive gas. FIG. 47F isa photograph in the case of adding CH₂Cl₂ as an additive gas.

As shown in FIG. 47A and FIG. 47B, it was confirmed that the by-product(SiCl₂) adhered to the exhaust pipe in the case of not adding anadditive gas and in the case of adding HCl as an additive gas. Inaddition, as shown in FIG. 47C and FIG. 47D, the adhesion of theby-product (SiCl₂) was not observed, but the adhesion of carbon wasobserved in the cases of adding C₂HCl₃ and CCl₄ as an additive gas.Meanwhile, as shown in FIG. 47E and FIG. 47F, neither the adhesion ofthe by-product (SiCl₂) nor the adhesion of carbon was observed in thecases of adding CH₃Cl and CH₂Cl₂ as an additive gas.

From the above-mentioned results, it was confirmed that, when at leastone of CH₃Cl or CH₂Cl₂ was added as an additive gas, the generation ofSiCl₂ was able to be avoided, and in addition, a situation in whichcarbon was precipitated in the exhaust pipe was able to be avoided.

EXAMPLE 5

A flow rate ratio given that the flow rate of MTS is defined as 1.0 isconsidered below. An experiment in which CH₃Cl was added as an additivegas and treatment was performed in a reforming furnace was performedthrough use of an apparatus similar to the apparatus of Example 4. Areaction furnace and the reforming furnace were under reduced pressure.In addition, a MTS/H₂/He mixed gas was supplied to the reaction furnaceas a raw material gas. The raw material gas had a flow rate ratio ofMTS:H₂:He=1:1:0.05. In addition, CH₃Cl was supplied to the reformingfurnace as an additive gas. Further, in order to consider a residencetime, the experiment was performed in the cases of inserting a tubeformed of carbon (hereinafter referred to as “carbon tube”) into thereforming furnace and not inserting the carbon tube into the reformingfurnace. The carbon tube has dimensions measuring 1.05 m in length, 60mm in outer diameter, and 20 mm in inner diameter. That is, when thereforming furnace is formed of a circular tube, the experiment wasperformed in the cases in which a specific surface area obtained bydividing the volume of the circular tube by the surface area of thecircular tube was 5 mm and 15 mm.

FIG. 48A, FIG. 48B, and FIG. 48C are each a graph for showing results ofExample 5. FIG. 48A is a graph for showing a relationship among theaddition amount of CH₃Cl, the temperature of the reforming furnace, andthe yield of a by-product. FIG. 48B is a graph for showing arelationship among the residence time of CH₃Cl, the temperature of thereforming furnace, and the yield of the by-product. FIG. 48C is a graphfor showing a relationship among the residence time of CH₃Cl, thetemperature of the reforming furnace, a flow rate ratio, and the yieldof the by-product.

In the case in which CH₃Cl was added at a flow rate ratio of 0.5 (in anamount of 50% of MTS) and the case in which CH₃Cl was added at a flowrate ratio of 1.0 (in the same amount as MTS), the yield (%) of theby-product (SiCl₂) at the time of changing the temperature of thereforming furnace was measured. As a result, in the case in which CH₃Clwas added to the reforming furnace at a flow rate ratio of 0.5(represented by black circles in FIG. 48A), it was confirmed that theyield of the by-product was decreased with an increase in temperature ofthe reforming furnace until the temperature of the reforming furnacereached 750° C. In addition, it was confirmed that a decrease rate ofthe yield of the by-product was decreased when the temperature of thereforming furnace exceeded 750° C.

In the case in which CH₃Cl was added to the reforming furnace at a flowrate ratio of 1.0 (in the same amount as MTS) (represented by blacksquares in FIG. 48A), it was confirmed that the yield of the by-productwas decreased with an increase in temperature of the reforming furnace.In addition, it was confirmed that no by-product was generated (theyield became 0%) when the temperature of the reforming furnace was 750°C. or more.

From the above-mentioned results, in the case of adopting CH₃Cl as anadditive gas, it was confirmed that the generation of the by-product(SiCl₂) was able to be prevented when the temperature of the reformingfurnace was set to 750° C. or more. In addition, when the temperature ofthe reforming furnace is 850° C. or more, a SiC film is formed.Accordingly, in the case of adopting CH₃Cl as an additive gas, it wasconfirmed that the temperature of the reforming furnace was preferablyset to 750° C. or more and less than 850° C.

In addition, in the cases in which the residence time of CH₃Cl in thereforming furnace was set to 0.080 second (the carbon tube was inserted)and 1.0 second (the carbon tube was not inserted), the yield (%) of theby-product (SiCl₂) at the time of changing the temperature of thereforming furnace was measured. As a result, in the case in which theresidence time in the reforming furnace was set to 0.080 second(represented by black circles in FIG. 48B), it was confirmed that theyield of the by-product was decreased with an increase in temperature ofthe reforming furnace.

Meanwhile, in the case in which the residence time in the reformingfurnace was set to 1.0 second (represented by black squares in FIG.48B), it was confirmed that the yield of the by-product was decreasedwith an increase in temperature of the reforming furnace. In addition,it was confirmed that no by-product was generated (the yield became 0%)when the temperature of the reforming furnace was 750° C. or more.

From the above-mentioned results, in the case of adopting CH₃Cl as anadditive gas, it was confirmed that the generation of the by-product wasable to be prevented when the residence time of the additive gas in thereforming furnace was set to 1.0 second or more. From the fact that adecreasing effect on the by-product was observed also when the residencetime was set to 0.080 second, it is presumed that, in the case ofadopting CH₃Cl as an additive gas, the generation of the by-product canbe prevented when the residence time of the additive gas in thereforming furnace is set to 0.2 second or more.

In addition, when the residence time of the additive gas in thereforming furnace is set to 10 seconds or more, the reforming furnaceitself is increased in size. Accordingly, in the case of adopting CH₃Clas an additive gas, it was confirmed that the residence time of theadditive gas in the reforming furnace was preferably set to 0.2 secondor more and less than 10 seconds. That is, when the residence time ofthe additive gas in the reforming furnace is set to 0.2 second or moreand less than 10 seconds, the generation of the by-product can beprevented while the reforming furnace can be reduced in size.

In addition, the yield (%) of the by-product (SiCl₂) at the time ofchanging a flow rate ratio between the additive gas (CH₃Cl) and MTS(additive gas/MTS) was measured. In the case in which the residence timeof CH₃Cl in the reforming furnace was set to 0.080 second and thetemperature of the reforming furnace was set to 975° C. (represented byblack circles in FIG. 48C), it was revealed that the yield of theby-product was decreased with an increase in flow rate ratio (ratio inamount of substance).

In the case in which the residence time of CH₃Cl in the reformingfurnace was set to 1.0 second and the temperature of the reformingfurnace was set to 975° C. (represented by black squares in FIG. 48C),it was revealed that the yield of the by-product was decreased with anincrease in flow rate ratio. In addition, it was confirmed that noby-product was generated (the yield became 0%) when the flow rate ratiowas 1.0 or more.

In the case in which the residence time of CH₃Cl in the reformingfurnace was set to 1.0 second and the temperature of the reformingfurnace was set to 750° C. (represented by white squares in FIG. 48C),it was revealed that the yield of the by-product was decreased with anincrease in flow rate ratio. In addition, it was confirmed that noby-product was generated (the yield became 0%) when the flow rate ratiowas 1.0 or more.

From the above-mentioned results, it was confirmed that the generationof the by-product (SiCl₂) was able to be prevented when the flow rateratio between CH₃Cl and MTS (CH₃Cl/MTS) was set to 1.0 or more.

EXAMPLE 6

A flow rate ratio given that the flow rate of MTS is defined as 1.0 isconsidered below. An experiment in which CH₂Cl₂ was added as an additivegas and treatment was performed in a reforming furnace was performedthrough use of an apparatus similar to the apparatus of Example 4. Areaction furnace and the reforming furnace were under reduced pressure.

In addition, a MTS/H₂/He mixed gas was supplied to the reaction furnaceas a raw material gas. The raw material gas had a flow rate ratio ofMTS:H₂:He=1:1:0.05. In addition, CH₂Cl₂ was supplied to the reformingfurnace as an additive gas. Further, in order to consider a residencetime, the experiment was performed in the cases of inserting a carbontube into the reforming furnace and not inserting the carbon tube intothe reforming furnace. The dimensions of the carbon tube are the same asin Example 5, i.e., 1.05 m in length, 60 mm in outer diameter, and 20 mmin inner diameter. That is, when the reforming furnace is formed of acircular tube, the experiment was performed in the cases in which aspecific surface area obtained by dividing the volume of the circulartube by the surface area of the circular tube was 5 mm and 15 mm.

FIG. 49A, FIG. 49B, and FIG. 49C are each a graph for showing results ofExample 6. FIG. 49A is a graph for showing a relationship among theaddition amount of CH₂Cl₂, the temperature of the reforming furnace, andthe yield of a by-product. FIG. 49B is a graph for showing arelationship among the residence time of CH₂Cl₂, the temperature of thereforming furnace, and the yield of the by-product. FIG. 49C is a graphfor showing a relationship among the residence time of CH₂Cl₂, thetemperature of the reforming furnace, a flow rate ratio, and the yieldof the by-product.

In the case in which CH₂Cl₂ was added at a flow rate ratio of 0.25 (inan amount of 25% of MTS), the case in which CH₂Cl₂ was added at a flowrate ratio of 0.5 (in an amount of 50% of MTS), and the case in whichCH₂Cl₂ was added at a flow rate ratio of 1.0 (in the same amount asMTS), the yield (%) of the by-product (SiCl₂) at the time of changingthe temperature of the reforming furnace was measured. As a result, inthe case in which CH₂Cl₂ was added to the reforming furnace at a flowrate ratio of 0.25 (represented by black squares in FIG. 49A), it wasconfirmed that the yield of the by-product was decreased with anincrease in temperature of the reforming furnace until the temperatureof the reforming furnace reached 750° C. In addition, it was confirmedthat no by-product was generated (the yield became 0%) when thetemperature of the reforming furnace was 750° C. or more and less than850° C. Meanwhile, it was confirmed that the yield of the by-product wasincreased when the temperature of the reforming furnace was 850° C. ormore.

In the case in which CH₂Cl₂ was added at a flow rate ratio of 0.5(represented by black circles in FIG. 49A), it was confirmed that theyield of the by-product was decreased with an increase in temperature ofthe reforming furnace until the temperature of the reforming furnacereached 750° C. In addition, it was confirmed that no by-product wasgenerated (the yield became 0%) when the temperature of the reformingfurnace was 750° C. or more.

In the case in which CH₂Cl₂ was added to the reforming furnace at a flowrate ratio of 1.0 (represented by white squares in FIG. 49A), it wasconfirmed that the yield of the by-product was decreased with anincrease in temperature of the reforming furnace. In addition, it wasconfirmed that no by-product was generated (the yield became 0%) whenthe temperature of the reforming furnace was 750° C. or more.

From the above-mentioned results, in the case of adopting CH₂Cl₂ as anadditive gas, it was confirmed that the generation of the by-product(SiCl₂) was able to be prevented when the temperature of the reformingfurnace was set to 750° C. or more and less than 850° C.

In addition, in the cases in which the residence time of CH₂Cl₂ in thereforming furnace was set to 0.080 second (the carbon tube was inserted)and 1.0 second (the carbon tube was not inserted), the yield (%) of theby-product (SiCl₂) at the time of changing the temperature of thereforming furnace was measured. As a result, in the case in which theresidence time in the reforming furnace was set to 0.080 second(represented by black circles in FIG. 49B), it was confirmed that theyield of the by-product was decreased with an increase in temperature ofthe reforming furnace until the temperature of the reforming furnacereached 975° C. In addition, it was confirmed that no by-product wasgenerated (the yield became 0%) when the temperature of the reformingfurnace was 975° C. Meanwhile, it was confirmed that the yield of theby-product was slightly increased (about 0.1%) when the temperature ofthe reforming furnace exceeded 975° C.

In the case in which the residence time in the reforming furnace was setto 1.0 second (represented by black squares in FIG. 49B), it wasconfirmed that the yield of the by-product was decreased with anincrease in temperature of the reforming furnace. In addition, it wasconfirmed that no by-product was generated (the yield became 0%) whenthe temperature of the reforming furnace was 750° C. or more.

From the above-mentioned results, in the case of adopting CH₂Cl₂ as anadditive gas, it was confirmed that the generation of the by-product(SiCl₂) was able to be prevented when the residence time of the additivegas in the reforming furnace was set to 0.080 second or more and lessthan 1.0 second and the temperature of the reforming furnace was set to975° C. or more and less than 1,100° C.

In addition, it was confirmed that the generation of the by-product(SiCl₂) was able to be prevented when the residence time of the additivegas in the reforming furnace was set to 1.0 second or more and thetemperature of the reforming furnace was set to 750° C. or more and lessthan 850° C. Further, as described above, when the residence time of theadditive gas in the reforming furnace is set to 10 seconds or more, thereforming furnace itself is increased in size. Accordingly, in the caseof adopting CH₂Cl₂ as an additive gas, when the residence time of theadditive gas in the reforming furnace is set to 1.0 second or more andless than 10 seconds and the temperature of the reforming furnace is setto 750° C. or more and less than 850° C., the generation of theby-product can be prevented while the reforming furnace can be reducedin size.

In addition, the yield (%) of the by-product (SiCl₂) at the time ofchanging a flow rate ratio between the additive gas (CH₂Cl₂) and MTS(additive gas/MTS) was measured. In the case in which the residence timeof CH₂Cl₂ in the reforming furnace was set to 0.080 second and thetemperature of the reforming furnace was set to 975° C. (represented byblack circles in FIG. 49C), it was confirmed that no by-product wasgenerated when the flow rate ratio (ratio in amount of substance) was 1or more.

In the case in which the residence time of CH₂Cl₂ in the reformingfurnace was set to 1.0 second and the temperature of the reformingfurnace was set to 975° C. (represented by black squares in FIG. 49C),it was revealed that the yield of the by-product was decreased with anincrease in flow rate ratio. In addition, it was confirmed that noby-product was generated when the flow rate ratio was 0.5 or more.

In the case in which the residence time of CH₂Cl₂ in the reformingfurnace was set to 0.080 seconds and the temperature of the reformingfurnace was set to 750° C. (represented by white circles in FIG. 49C),it was revealed that the yield of the by-product was decreased with anincrease in flow rate ratio.

In the case in which the residence time of CH₂Cl₂ in the reformingfurnace was set to 1.0 second and the temperature of the reformingfurnace was set to 750° C. (represented by white squares in FIG. 49C),it was revealed that the yield of the by-product was decreased with anincrease in flow rate ratio. In addition, it was confirmed that noby-product was generated when the flow rate ratio was 0.25 or more.

From the above-mentioned results, it was confirmed that the generationof the by-product (SiCl₂) was able to be prevented when the flow rateratio between CH₂Cl₂ and MTS (CH₂Cl₂/MTS) was set to 0.5 or more.

FIG. 50A, FIG. 50B, and FIG. 50C are each a photograph of an exhaustpipe (a pipe connected to the outlet of the reforming furnace) inExamples 5 and 6. FIG. 50A is a photograph in the case of not adding anadditive gas. FIG. 50B is a photograph in the case of adding CH₃Cl as anadditive gas. FIG. 50C is a photograph in the case of adding CH₂Cl₂ asan additive gas. FIG. 50A, FIG. 50B, and FIG. 50C are each thephotograph of the exhaust pipe in the case in which the temperature ofthe reforming furnace is set to 750° C.

As shown in FIG. 50A, in the case of not adding an additive gas, it wasconfirmed that the by-product (SiCl₂) was accumulated in the exhaustpipe. In addition, as shown in FIG. 50B, in the case of adding CH₃Cl asan additive gas, it was confirmed that a highly acidic (non-ignitible)substance different from SiCl₂ was precipitated. Meanwhile, as shown inFIG. 50C, in the case of adding CH₂Cl₂ as an additive gas, neither theadhesion of the by-product (SiCl₂) nor the adhesion of other substanceswas observed.

Apparatus 100 for Producing Silicon Compound Material

FIG. 51 is a view for illustrating an apparatus 100 for producing asilicon compound material according to this embodiment. As illustratedin FIG. 51, the apparatus 100 for producing a silicon compound materialincludes a reaction furnace 110, a raw material gas supply portion 120,a reforming furnace 130, and an additive gas supply portion 140. In FIG.51, a flow of a gas is represented by the arrow of a solid line.

The reaction furnace 110 was retained at a predetermined temperature anda predetermined pressure (reduced pressure). A preform is housed in thereaction furnace 110. A raw material gas is supplied to the reactionfurnace 110 from the raw material gas supply portion 120. The rawmaterial gas contains methyltrichlorosilane (MTS). In the reactionfurnace 110, the preform is infiltrated with silicon carbide.

A gas discharged from the reaction furnace 110 is supplied to thereforming furnace 130 through a pipe 112. The reforming furnace 30 isconfigured to retain the gas discharged from the reaction furnace 110 at200° C. or more and less than 1,100° C. The additive gas supply portion140 is configured to supply an additive gas to the reforming furnace130. The additive gas is one or more selected from the group consistingof CH₃Cl (chloromethane), CH₂Cl₂ (dichloromethane), CCl₄ (carbontetrachloride), C₂H₃Cl₃ (trichloroethane), and C₂HCl₃(trichloroethylene).

When the additive gas is added to the gas discharged from the reactionfurnace 110 and the gas discharged from the reaction furnace 110 isretained at 200° C. or more and less than 1,100° C. in the reformingfurnace 130, the generation of SiCl₂ can be prevented. With this, asituation in which SiCl₂ adheres to an exhaust pipe to be connected to asubsequent stage of the reforming furnace 130 can be avoided.Accordingly, the reforming furnace 130 and the exhaust pipe can bewashed easily. As a result, a burden and cost for maintenance of anexhaust passage from the reaction furnace 110 can be reduced, and byextension, a safe operation can be performed.

The additive gas is preferably any one or both of CH₃Cl and CH₂Cl₂. Whenthe additive gas is any one or both of CH₃Cl and CH₂Cl₂, a situation inwhich carbon is precipitated in the exhaust pipe can be avoided.

In addition, when the additive gas supply portion 140 is configured toadd CH₃Cl, the reforming furnace 130 is configured to retain the gasdischarged from the reaction furnace 110 and the additive gas at 750° C.or more and less than 850° C. In the case of adding CH₃Cl, when thetemperature of the reforming furnace 130 is set to 750° C. or more, thegeneration of SiCl₂ can be prevented. In addition, when the temperatureof the reforming furnace 130 is 850° C. or more, a SiC film is formed.Accordingly, in the case of adding CH₃Cl, when the temperature of thereforming furnace 130 is set to 750° C. or more and less than 850° C.,the generation of SiCl₂ can be prevented while the maintenanceproperties of the reforming furnace 130 are improved.

Further, when the additive gas supply portion 140 is configured to addCH₃Cl, the residence time of CH₃Cl in the reforming furnace 130 is setto 0.2 second or more and less than 10 seconds. When the residence timeis set to 0.2 second or more, the generation of SiCl₂ can be prevented.In addition, when the residence time is set to less than 10 seconds, thereforming furnace 130 can be reduced in size.

In addition, when the additive gas supply portion 140 is configured toadd CH₃Cl, CH₃Cl is added so that a flow rate ratio between CH₃Cl andMTS to be supplied from the raw material gas supply portion 120(CH₃Cl/MTS) is 1.0 or more. With this, the generation of SiCl₂ can beprevented.

Meanwhile, when the additive gas supply portion 140 is configured to addCH₂Cl₂, the reforming furnace 130 is configured to retain the gasdischarged from the reaction furnace 110 and the additive gas at 750° C.or more and less than 850° C. In the case of adding CH₂Cl₂, when thetemperature of the reforming furnace 130 is set to 750° C. or more, thegeneration of SiCl₂ can be prevented. In addition, when the temperatureof the reforming furnace 130 is 850° C. or more, a SiC film is formed.Accordingly, in the case of adding CH₂Cl₂, when the temperature of thereforming furnace 130 is set to 750° C. or more and less than 850° C.,the generation of SiCl₂ can be prevented while the maintenanceproperties of the reforming furnace 130 are improved.

In this case, the residence time of CH₂Cl₂ in the reforming furnace 130is set to 0.2 second or more and less than 10 seconds. When theresidence time is set to 0.2 second or more, the generation of SiCl₂ canbe prevented. In addition, when the residence time is set to less than10 seconds, the reforming furnace 130 can be reduced in size.

In addition, when the additive gas supply portion 140 is configured toadd CH₂Cl₂, CH₂Cl₂ is added so that a flow rate ratio between CH₂Cl₂ andMTS to be supplied from the raw material gas supply portion 120(CH₂Cl₂/MTS) is 0.25 or more, preferably 0.5 or more. With this, thegeneration of SiCl₂ can be prevented.

In addition, a baffle plate may be arranged in the reforming furnace130. FIG. 52 is a view for illustrating a modified example of thereforming furnace 130. As illustrated in FIG. 52, a main body 132 of thereforming furnace 130 has a tubular shape (e.g., a circular tube shape).The main body 132 is a furnace of a hot wall type heated from an outsidewith a heating device (not shown). A plurality of baffle plates 134 arearranged in the main body 132. The baffle plates 134 are each asemicircular plate member extending from an inner peripheral surface ofthe main body 132 to a center thereof. The baffle plates 134 arearranged in the main body 132 at different positions in a gas flowdirection (an extending direction of the main body 132). In addition,the baffle plates 134 adjacent to each other are arranged in the mainbody 132 so that their connecting positions to the main body 132 aredifferent from each other.

Through arrangement of the baffle plates 134, the gas discharged fromthe reaction furnace 110 and the additive gas can be mixed with eachother efficiently. Accordingly, the generation of SiCl₂ can beprevented.

As described above, the apparatus 100 for producing a silicon compoundmaterial according to this embodiment enables prevention of thegeneration of SiCl₂ with a simple configuration of adding the additivegas.

The embodiment has been described above with reference to the attacheddrawings, but, needless to say, the present disclosure is not limited tothe embodiment. It is apparent that those skilled in the art may arriveat various alternations and modifications within the scope of claims,and those examples are construed as naturally falling within thetechnical scope of the present disclosure.

For example, in the above-mentioned embodiment, when the additive gassupply portion 140 of the apparatus 100 for producing a silicon compoundmaterial is configured to add CH₂Cl₂, the reforming furnace 130 isconfigured to retain the gas discharged from the reaction furnace 110and the additive gas at 750° C. or more and less than 850° C. However,when the additive gas supply portion 140 is configured to add CH₂Cl₂,the reforming furnace 130 may retain the gas discharged from thereaction furnace 110 and the additive gas at 975° C. or more and lessthan 1,000° C. In this case, the residence time of CH₂Cl₂ in thereforming furnace 130 is desirably set to 0.080 second or more and lessthan 0.2 second. With this, the generation of SiCl₂ can be prevented.

In addition, in the above-mentioned embodiment, the description has beenmade taking as an example a configuration in which the apparatus 100 forproducing a silicon compound material includes the additive gas supplyportion 140. However, the additive gas supply portion 140 is not anessential constituent component. When the apparatus for producing asilicon compound material does not include the additive gas supplyportion 140, the reforming furnace 130 is desirably configured to retainthe gas discharged from the reaction furnace 110 at a predeterminedtemperature of 500° C. or more and less than 950° C. With this, thegeneration of SiCl₂ can be prevented.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to a method of producing a siliconcompound material and to an apparatus for producing a silicon compoundmaterial.

REFERENCE SIGNS LIST

-   100 apparatus for producing silicon compound material-   110 reaction furnace-   120 raw material gas supply portion-   130 reforming furnace-   134 baffle plate-   140 additive gas supply portion

What is claimed is:
 1. A method of producing a silicon compoundmaterial, comprising the steps of: storing a silicon carbide preform ina reaction furnace; supplying a raw material gas containingmethyltrichlorosilane to the reaction furnace to infiltrate the preformwith silicon carbide; and controlling and changing a temperature of agas discharged from the reaction furnace at a predetermined rate tosubject the gas to continuous thermal history, to thereby decreasegeneration of a liquid or solid by-product derived from the gas.
 2. Amethod of producing a silicon compound material according to claim 1,wherein the step of controlling and changing a temperature of a gasdischarged from the reaction furnace at a predetermined rate comprises astep of retaining the gas discharged from the reaction furnace at apredetermined temperature.
 3. A method of producing a silicon compoundmaterial according to claim 2, wherein the predetermined temperaturefalls within a range of 500° C. or more and less than 950° C. or is1,500° C. or more.
 4. A method of producing a silicon compound materialaccording to claim 3, wherein the predetermined temperature falls withina range of 600° C. or more and less than 800° C.
 5. A method ofproducing a silicon compound material according to claim 1, wherein thestep of decreasing generation of a liquid or solid by-product comprisesretaining the gas discharged from the reaction furnace at apredetermined temperature for a predetermined time period falling withina range of from 0 seconds to 8 seconds.
 6. A method of producing asilicon compound material according to claim 2, wherein the step ofdecreasing generation of a liquid or solid by-product comprisesretaining the gas discharged from the reaction furnace at apredetermined temperature for a predetermined time period falling withina range of from 0 seconds to 8 seconds.
 7. A method of producing asilicon compound material according to claim 3, wherein the step ofdecreasing generation of a liquid or solid by-product comprisesretaining the gas discharged from the reaction furnace at apredetermined temperature for a predetermined time period falling withina range of from 0 seconds to 8 seconds.
 8. A method of producing asilicon compound material according to claim 4, wherein the step ofdecreasing generation of a liquid or solid by-product comprisesretaining the gas discharged from the reaction furnace at apredetermined temperature for a predetermined time period falling withina range of from 0 seconds to 8 seconds.
 9. A method of producing asilicon compound material according to claim 1, wherein the step ofdecreasing generation of a liquid or solid by-product comprises changingthe temperature of the gas to a plurality of temperatures in a stepwisemanner.
 10. A method of producing a silicon compound material accordingto claim 2, wherein the step of decreasing generation of a liquid orsolid by-product comprises changing the temperature of the gas to aplurality of temperatures in a stepwise manner.
 11. A method ofproducing a silicon compound material according to claim 3, wherein thestep of decreasing generation of a liquid or solid by-product compriseschanging the temperature of the gas to a plurality of temperatures in astepwise manner.
 12. A method of producing a silicon compound materialaccording to claim 4, wherein the step of decreasing generation of aliquid or solid by-product comprises changing the temperature of the gasto a plurality of temperatures in a stepwise manner.
 13. A method ofproducing a silicon compound material according to claim 1, wherein theliquid or solid by-product comprises a higher-chlorosilane.
 14. A methodof producing a silicon compound material according to claim 2, whereinthe liquid or solid by-product comprises a higher-chlorosilane.
 15. Amethod of producing a silicon compound material according to claim 3,wherein the liquid or solid by-product comprises a higher-chlorosilane.16. A method of producing a silicon compound material according to claim4, wherein the liquid or solid by-product comprises ahigher-chlorosilane.
 17. A method of producing a silicon compoundmaterial according to claim 1, wherein the step of decreasing generationof a liquid or solid by-product comprises converting SiCl₂ serving as aprecursor of the liquid or solid by-product into a stable substance, tothereby decrease the generation of the liquid or solid by-product.
 18. Amethod of producing a silicon compound material according to claim 2,wherein the step of decreasing generation of a liquid or solidby-product comprises converting SiCl₂ serving as a precursor of theliquid or solid by-product into a stable substance, to thereby decreasethe generation of the liquid or solid by-product.
 19. A method ofproducing a silicon compound material according to claim 3, wherein thestep of decreasing generation of a liquid or solid by-product comprisesconverting SiCl₂ serving as a precursor of the liquid or solidby-product into a stable substance, to thereby decrease the generationof the liquid or solid by-product.
 20. A method of producing a siliconcompound material according to claim 4, wherein the step of decreasinggeneration of a liquid or solid by-product comprises converting SiCl₂serving as a precursor of the liquid or solid by-product into a stablesubstance, to thereby decrease the generation of the liquid or solidby-product.
 21. A method of producing a silicon compound materialaccording to claim 17, wherein the stable substance comprises at leastone of methyltrichlorosilane, dimethyldichlorosilane, disilane,dichlorosilane, trichlorosilane, or tetrachlorosilane.
 22. A method ofproducing a silicon compound material according to claim 1, wherein thestep of decreasing generation of a liquid or solid by-product comprisesadding a predetermined additive gas to the gas discharged from thereaction furnace.
 23. A method of producing a silicon compound materialaccording to claim 22, wherein the step of decreasing generation of aliquid or solid by-product comprises adding the additive gas so that anamount of substance of the additive gas is larger than an amount ofsubstance of the liquid or solid by-product.
 24. A method of producing asilicon compound material according to claim 22, wherein the step ofdecreasing generation of a liquid or solid by-product comprises addingchlorine so that an amount of substance of chlorine is larger than anamount of substance of silicon contained in the liquid or solidby-product.
 25. A method of producing a silicon compound materialaccording claim 22, wherein the step of decreasing generation of aliquid or solid by-product comprises a step of retaining the gasdischarged from the reaction furnace at a predetermined temperature, andwherein the step of retaining the gas discharged from the reactionfurnace at a predetermined temperature comprises the adding apredetermined additive gas.
 26. A method of producing a silicon compoundmaterial according to claim 25, wherein the step of retaining the gasdischarged from the reaction furnace at a predetermined temperaturecomprises using a reforming furnace, and wherein a time period for whichthe gas discharged from the reaction furnace is retained at thepredetermined temperature is a residence time of the gas in thereforming furnace.
 27. A method of producing a silicon compound materialaccording to claim 25, wherein the predetermined temperature fallswithin a range of 200° C. or more and less than 1,100° C.
 28. A methodof producing a silicon compound material according to claim 25, whereinthe predetermined temperature falls within a range of 750° C. or moreand less than 850° C.
 29. A method of producing a silicon compoundmaterial according to claim 22, wherein the additive gas comprises a gasincluding a molecule containing chlorine.
 30. A method of producing asilicon compound material according to claim 22, wherein the additivegas comprises at least one of a nitrogen gas, a hydrogen gas, hydrogenchloride, chloromethane, tetrachloromethane, trichloroethylene,trichloroethane, ethylene, ethanol, acetone, methanol, water vapor,dichloromethane, or chloroform.
 31. A method of producing a siliconcompound material according to claim 25, wherein the additive gascomprises chloromethane or dichloromethane, and wherein, in the step ofretaining the gas discharged from the reaction furnace at apredetermined temperature, a time period for which the gas dischargedfrom the reaction furnace, to which the additive gas has been added, isretained at the predetermined temperature is set to 0.08 second or more.32. A method of producing a silicon compound material according to claim25, wherein the additive gas comprises chloromethane or dichloromethane,and wherein, in the step of retaining the gas discharged from thereaction furnace at a predetermined temperature, a time period for whichthe gas discharged from the reaction furnace, to which the additive gashas been added, is retained at the predetermined temperature is set to 1second or more.
 33. A method of producing a silicon compound materialaccording to claim 25, wherein the additive gas comprises chloromethane,and wherein, in the step of retaining the gas discharged from thereaction furnace at a predetermined temperature, an amount of substanceof chloromethane to be added is 1.0 time or more as large as an amountof substance of methyltrichlorosilane in the raw material gas to beloaded.
 34. A method of producing a silicon compound material accordingto claim 25, wherein the additive gas comprises chloromethane, andwherein, in the step of retaining the gas discharged from the reactionfurnace at a predetermined temperature, the predetermined temperaturefalls within a range of 750° C. or more and less than 850° C., an amountof substance of chloromethane to be added falls within a range of 1.0time or more and less than 1.5 times as large as a loading amount ofmethyltrichlorosilane in the raw material gas, and a time period forwhich the gas discharged from the reaction furnace, to which theadditive gas has been added, is retained at the predeterminedtemperature is set within a range of 1 second or more and less than 10seconds.
 35. A method of producing a silicon compound material accordingto claim 25, wherein the additive gas comprises dichloromethane, andwherein, in the step of retaining the gas discharged from the reactionfurnace at a predetermined temperature, an amount of substance ofdichloromethane to be added is 0.25 time or more as large as a loadingamount of methyltrichlorosilane in the raw material gas.
 36. A method ofproducing a silicon compound material according to claim 25, wherein theadditive gas comprises dichloromethane, and wherein, in the step ofretaining the gas discharged from the reaction furnace at apredetermined temperature, the predetermined temperature falls within arange of 750° C. or more and less than 850° C., an amount of substanceof dichloromethane to be added falls within a range of 0.25 time or moreand less than 1.5 times as large as an amount of substance ofmethyltrichlorosilane in the raw material gas to be loaded, and a timeperiod for which the gas discharged from the reaction furnace, to whichthe additive gas has been added, is retained at the predeterminedtemperature is set within a range of 1 second or more and less than 10seconds.
 37. A method of producing a silicon compound material accordingto claim 25, wherein the additive gas comprises any one of hydrogenchloride, tetrachloromethane, trichloroethylene, trichloroethane, andethylene, wherein the predetermined temperature is 975° C., wherein anamount of substance of the additive gas to be added is 1.0 time as largeas an amount of substance of methyltrichlorosilane in the raw materialgas to be loaded, and wherein a time period for which the gas dischargedfrom the reaction furnace, to which the additive gas has been added, isretained at the predetermined temperature is set to 1 second.
 38. Anapparatus for producing a silicon compound material, comprising: areaction furnace configured to store a preform; a raw material gassupply portion configured to supply a raw material gas containingmethyltrichlorosilane to the reaction furnace; a reforming furnaceconfigured to retain a gas discharged from the reaction furnace at apredetermined temperature; and an additive gas supply portion configuredto supply a predetermined additive gas to the reforming furnace.
 39. Anapparatus for producing a silicon compound material according to claim38, wherein the reforming furnace is of a hot wall type.
 40. Anapparatus for producing a silicon compound material according to claim38, wherein the reforming furnace has arranged therein a baffle plate.41. An apparatus for producing a silicon compound material according toclaim 38, wherein the reforming furnace is formed of a circular tube,and wherein the circular tube has a specific surface area falling withina range of from 5 mm to 15 mm, which is determined by dividing a volumeof the circular tube by a surface area of the circular tube.